docs: reflect changes to changelog

BREAKING CHANGE: Consumers must use ESM-compatible environments.
All import paths now include .js extensions.
CommonJS (require) is no longer supported.

.github/workflows/CreateRelease.yml

@@ -4,6 +4,7 @@ on:
     push:
         branches:
             - main
+            - 'dev/*'
         paths:
             - 'package.json'
     workflow_dispatch: # Allows manual execution of the workflow.
@@ -22,20 +23,14 @@ jobs:
               with:
                   node-version: '20.8.0'
 
-            - name: Install Dependencies
-              run: npm install
-
-            - name: Run Tests
-              run: npm run test:verbose
-
-            - name: Build the Project
-              run: npm run build:tsc
+            - name: Install dependencies, run tests and build
+              run: npm run prepare:deploy
 
             - name: Get the version
               id: get_version
               run: |
                   VERSION=$(npm run version:show | tail -n 1)
-                  echo "VERSION=$VERSION" >> $GITHUB_ENV
+                  echo "VERSION=v$VERSION" >> $GITHUB_ENV
               shell: bash
 
             - name: Get previous release tag
@@ -77,8 +72,9 @@ jobs:
                   echo "Generating release notes from ${{ env.PREVIOUS_TAG }} to HEAD..."
                   repo_url=$(git config --get remote.origin.url)
                   notes=$(git log ${{ env.PREVIOUS_TAG }}..HEAD --pretty=format:"- [\`%h\`]($repo_url/commit/%H): %s%n")
-                  echo "Release notes:"
+                  echo "See [CHANGELOG.md](./CHANGELOG.md) for more details."
                   echo "$notes"
+                  echo ""
                   echo "### Changes in this release" > release_notes.md
                   echo "$notes" >> release_notes.md
               shell: bash
@@ -90,17 +86,6 @@ jobs:
                   git config --local user.email "actions@github.com"
               shell: bash
 
-            # - name: Create temporary branch
-            #   id: create_temp_branch
-            #   if: steps.check_version.outputs.skip_release == 'false'
-            #   run: |
-            #       git checkout --orphan release/v${{ env.VERSION }}
-            #       git reset
-            #       rm -f .gitignore
-            #       git add README.md package.json LICENSE dist/ src/ tsconfig.json
-            #       git commit -m "Prepare files for release ${{ env.VERSION }}"
-            #   shell: bash
-
             - name: Create and push tag
               id: create_tag
               if: steps.check_version.outputs.skip_release == 'false'
@@ -111,6 +96,15 @@ jobs:
                   GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
               shell: bash
 
+            - name: Set Release Prerelease Flag
+              id: set_prerelease_flag
+              run: |
+                  if [[ "${{ github.ref }}" == "refs/heads/main" ]]; then
+                    echo "PRE_RELEASE=false" >> $GITHUB_ENV
+                  elif [[ "${{ github.ref }}" == refs/heads/dev/* ]]; then
+                    echo "PRE_RELEASE=true" >> $GITHUB_ENV
+                  fi
+
             - name: Release
               if: steps.check_version.outputs.skip_release == 'false'
               uses: softprops/action-gh-release@v2
@@ -118,6 +112,6 @@ jobs:
                   tag_name: ${{ env.VERSION }}
                   name: Release ${{ env.VERSION }}
                   body_path: release_notes.md
-                  prerelease: true
+                  prerelease: ${{ env.PRE_RELEASE }}
               env:
                   GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/ValidateBranchName.yml

@@ -3,7 +3,7 @@ name: Validate Branch Name on Pull Request
 on:
     pull_request:
         branches:
-            - main
+            - UNDEFINED
 
 jobs:
     validate-branch-name-on-pull-request:

CHANGELOG.md

@@ -0,0 +1,148 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+
+### Deprecated
+
+### Removed
+
+### Fixed
+
+### Security
+
+## [1.1.0]
+
+### Added
+
+-   feat: exported `inject()` function from the public API via `index.ts`  
+    The function is now available as part of the main module exports.
+
+## [1.0.0]
+
+### Added
+
+-   feat: Enable native ESM support using `"type": "module"` and `moduleResolution: "NodeNext"` in the compiler settings.
+-   feat: All internal imports now explicitly include `.js` extensions for full Node.js ESM compatibility.
+-   feat: Updated `tsconfig.json` to reflect changes for ESM builds (`module: "NodeNext"`, `target: "ES2020"`, etc.).
+-   feat(cli): add `--without-extension` (`-x`) flag to optionally omit file extensions in generated import paths
+-   feat: introduce `inject()` function as a programmatic alternative to the `@Inject` decorator  
+    Supports optional initializers and constructor instantiation for resolved dependencies.  
+    Designed for cases where decorators are not suitable or dynamic resolution is needed.
+-   test: added comprehensive test suite for `inject()` function, covering resolution, initialization, error cases and instantiation behavior
+
+### Changed
+
+-   All source files using relative or internal imports were updated to use `.js` extensions to support Node.js ESM runtime resolution.
+-   test: update Jest config for ts-jest ESM compatibility and .js import support
+-   renamed internal parameter `necessary` → `isNecessary` for naming clarity
+
+### Removed
+
+-   Removed implicit support for CommonJS-style imports without file extensions.
+
+### Deprecated
+
+-   Support for CommonJS consumers using `require()` is no longer available. Use `import` with an ESM-compatible environment instead.
+
+### Fixed
+
+### Security
+
+### ⚠️ Breaking Changes
+
+-   **BREAKING CHANGE**: This version migrates the entire codebase to native ES modules.
+    -   Consumers must use Node.js in ESM mode or compatible bundlers.
+    -   Import paths now include `.js` extensions.
+    -   Using `require()` (CommonJS) to load this library will no longer work.
+    -   All consuming projects must either:
+        -   Use `"type": "module"` in their `package.json`, or
+        -   Use an ESM-aware bundler (e.g. Webpack, Vite, etc.)
+
+## [0.4.0]
+
+### Added
+
+-   feat: Export ImplementsStatic helper function
+
+### Deprecated
+
+### Removed
+
+### Fixed
+
+### Security
+
+## [0.3.0]
+
+### Added
+
+-   refactor: consolidate registration decorators
+    Introduced Register decorator to handle class and instance registration in the DI container.
+    Deprecated RegisterInstance in favor of Register, which now internally handles instance registration.
+    Added support for marking dependencies as deprecated with a warning logged upon first resolution.
+    Updated documentation with examples and notes on deprecation.
+-   tests: add mode parameter to RegisterInstanceDecorator
+    Introduced a mode parameter to the test_RegisterInstanceDecorator function allowing 'instance' or 'standalone' modes.
+    Updated test cases to utilize the new mode parameter when registering an instance.
+    Disabled specific ESLint rule in Decorators.test.ts for deprecation warnings.
+    Added an additional test call to test_RegisterInstanceDecorator with 'instance' mode.
+-   refactor: add region tags for overloads in Register.ts
+
+## [0.2.0]
+
+### Added
+
+-   Add pre release building to release workflow on dev/\* branches an version changes.
+-   feat: Introduced a new CLI command `tsinjex-generate` to automate the generation of import statements for registered dependencies.  
+    The command scans `.ts` files for `@Register` and `@RegisterInstance` decorators and generates an `auto-imports.ts` file.  
+    This ensures that all registered dependencies are automatically included without requiring manual imports.  
+    The CLI can be executed via `npx tsinjex-generate` or added as a script in `package.json` for easier integration.
+
+### Deprecated
+
+### Removed
+
+### Fixed
+
+### Security
+
+## [0.0.14]
+
+### Added
+
+-   Added **ChangeLog** file and format it according to [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
+-   Added reference to **Semantic Versioning** in the changelog file. (History will be updated on time).
+-   Version format is now `v0.0.0` instead of `0.0.0`. Changes to this are also reflected in the workflos.
+-   Add `Identifiers` and `Jest` Sections to the `README.md` file.
+-   feat: Add new Error `InitializationError` to reflect errors during initialization of a dependency.
+-   feat: Add initialization error handling and refactor Inject.
+-   feat: After injecting a dependency, the lazzy loading getter will be replaced with the dependency itself.
+-   feat: remove the use of a private property to store the injected dependencies. Now the dependencies are stored in the property itself.
+-   test: Add tests for the new features.
+
+### Deprecated
+
+-   Deprecated the old version format `0.0.0`.
+
+### Removed
+
+### Fixed
+
+### Security
+
+---
+
+[unreleased]: https://github.com/20Max01/TSinjex/compare/v1.0.0...HEAD
+[1.1.0]: https://github.com/20Max01/TSinjex/compare/v1.0.0...v1.1.0
+[1.0.0]: https://github.com/20Max01/TSinjex/compare/v0.4.0...v1.0.0
+[0.4.0]: https://github.com/20Max01/TSinjex/compare/v0.3.0...v0.4.0
+[0.3.0]: https://github.com/20Max01/TSinjex/compare/v0.2.0...v0.3.0
+[0.2.0]: https://github.com/20Max01/TSinjex/compare/v0.0.14...v0.2.0
+[0.0.14]: https://github.com/20Max01/TSinjex/compare/v0.0.13...v0.0.14

README.md

@@ -6,8 +6,14 @@
 
 ## Configuration
 
+### Identifiers
+
+Strings and symbols are possible for the **identifiers**.
+
 ### Jest
 
+For the use of TSinjex with Jest, the corresponding source files can be found under `./src` of the TSinjex node_module folder. To use these files, the `moduleNameMapper` must be configured in the Jest configuration file. The following example shows how to configure the Jest configuration file to use the source files of TSinjex.
+
 #### Example jest setup
 
 ```ts

bin/generate-imports.cjs

@@ -0,0 +1,122 @@
+#!/usr/bin/env node
+
+const fs = require('fs');
+const path = require('path');
+const yargs = require('yargs');
+
+// CLI argument parsing
+const argv = yargs
+  .option('src', {
+    alias: 's',
+    type: 'string',
+    description: 'Directory to search for files',
+    default: 'src',
+  })
+  .option('output', {
+    alias: 'o',
+    type: 'string',
+    description: 'Path to the output file',
+    default: 'src/auto-imports.ts',
+  })
+  .option('pattern', {
+    alias: 'p',
+    type: 'string',
+    description: 'File pattern to search for (e.g., .ts, .js)',
+    default: '.ts',
+  })
+  .option('without-extension', {
+    alias: 'x',
+    type: 'boolean',
+    description: 'Omit file extension in import paths',
+    default: false,
+  })
+  .help()
+  .argv;
+
+// Fixed RegEx patterns for decorator detection
+const SEARCH_PATTERNS = [
+  /^@Register(?:<(.+)?>)?\(\s*["']{1}(.+)?["']{1}\s*,?\s*(true|false)?\s*\)/m,
+  /^@RegisterInstance(?:<(.+)?>)?\(\s*["']{1}(.+)?["']{1}\s*,?\s*(.+)?\s*\)/m,
+];
+
+const FILE_PATTERN = argv.pattern.startsWith('.') ? argv.pattern : `.${argv.pattern}`;
+
+/**
+ * Recursively collects all files with a specific extension.
+ * @param {string} dirPath - Root directory
+ * @returns {string[]} List of file paths
+ */
+function getAllFiles(dirPath) {
+  let files = fs.readdirSync(dirPath);
+  let arrayOfFiles = [];
+
+  files.forEach((file) => {
+    const fullPath = path.join(dirPath, file);
+    if (fs.statSync(fullPath).isDirectory()) {
+      arrayOfFiles = arrayOfFiles.concat(getAllFiles(fullPath));
+    } else if (file.endsWith(FILE_PATTERN)) {
+      arrayOfFiles.push(fullPath);
+    }
+  });
+
+  return arrayOfFiles;
+}
+
+/**
+ * Checks files for decorator usage.
+ * @param {string[]} files
+ * @returns {string[]} Filtered files
+ */
+function findFilesWithPattern(files) {
+  return files.filter((file) => {
+    const content = fs.readFileSync(file, 'utf8');
+    return SEARCH_PATTERNS.some((pattern) => pattern.test(content));
+  });
+}
+
+/**
+ * Generates ES-style import statements from file paths.
+ * @param {string[]} files
+ * @returns {string}
+ */
+function generateImports(files) {
+  return files.map((file) => {
+    const relative = './' + path.relative(argv.src, file).replace(/\\/g, '/');
+    const noExt = relative.replace(FILE_PATTERN, '');
+    const finalPath = argv['without-extension'] ? noExt : `${noExt}${FILE_PATTERN}`;
+    return `import '${finalPath}';`;
+  }).join('\n') + '\n';
+}
+
+/**
+ * Script entry point.
+ */
+function main() {
+  try {
+    const srcDir = path.resolve(process.cwd(), argv.src);
+    const outputFile = path.resolve(process.cwd(), argv.output);
+
+    if (!fs.existsSync(srcDir)) {
+      console.error(`❌ Error: The directory '${srcDir}' does not exist.`);
+      process.exit(1);
+    }
+
+    const allFiles = getAllFiles(srcDir);
+    const filesWithPattern = findFilesWithPattern(allFiles);
+
+    if (filesWithPattern.length === 0) {
+      console.log(`ℹ️ No ${FILE_PATTERN} files found matching the specified decorator patterns.`);
+      return;
+    }
+
+    const importContent = generateImports(filesWithPattern);
+    fs.writeFileSync(outputFile, importContent);
+
+    console.log(`✅ Imports successfully generated: ${outputFile}`);
+  } catch (error) {
+    console.error('❌ An error occurred:', error.message);
+    process.exit(1);
+  }
+}
+
+main();

jest.config.cjs

@@ -2,11 +2,17 @@ module.exports = {
     setupFilesAfterEnv: ['./scripts/jest.setup.js'],
     preset: 'ts-jest',
     testEnvironment: 'node',
+    extensionsToTreatAsEsm: ['.ts'],
+    transform: {
+        '^.+\\.ts$': ['ts-jest', { useESM: true }],
+    },
     testMatch: ['**/__tests__/**/*.test.ts', '**/?(*.)+(test).ts'],
     testPathIgnorePatterns: ['\\.spec\\.ts$', '\\.performance\\.test\\.ts$'],
     moduleDirectories: ['node_modules', 'src'],
     moduleNameMapper: {
+        '^src/(.*)\\.js$': '<rootDir>/src/$1',
         '^src/(.*)$': '<rootDir>/src/$1',
+        '^(\\.{1,2}/.*)\\.js$': '$1',
     },
     collectCoverage: true,
     coverageDirectory: '.locale/coverage',
@@ -19,4 +25,4 @@ module.exports = {
             statements: 70,
         },
     },
-};
+};

jest.config.coverage.cjs

@@ -1,23 +1,32 @@
 module.exports = {
     setupFilesAfterEnv: ['./scripts/jest.setup.js'],
-    preset: 'ts-jest',
     testEnvironment: 'node',
+    transform: {
+        '^.+\\.ts$': ['ts-jest', { useESM: true }],
+    },
+    extensionsToTreatAsEsm: ['.ts'],
     testMatch: ['**/__tests__/**/*.test.ts', '**/?(*.)+(test).ts'],
     testPathIgnorePatterns: ['\\.spec\\.ts$', '\\.performance\\.test\\.ts$'],
     moduleDirectories: ['node_modules', 'src'],
     moduleNameMapper: {
+        '^src/(.*)\\.js$': '<rootDir>/src/$1',
         '^src/(.*)$': '<rootDir>/src/$1',
+        '^(\\.{1,2}/.*)\\.js$': '$1',
     },
     collectCoverage: true,
     coverageDirectory: '.locale/coverage',
-    coverageReporters: ['text', ['lcov', { projectRoot: '..' }], 'json-summary'],
+    coverageReporters: [
+        'text',
+        ['lcov', { projectRoot: '..' }],
+        'json-summary',
+    ],
     collectCoverageFrom: [
         'src/**/*.{ts,tsx}',
         '!src/**/*.d.ts',
         '!src/**/*.performance.test.ts',
         '!src/**/*.spec.ts',
         '!src/**/*.test.ts',
-        '!src/auto-imports.ts'
+        '!src/auto-imports.ts',
     ],
     coverageThreshold: {
         global: {

package-lock.json

@@ -1,17 +1,20 @@
 {
   "name": "ts-injex",
-  "version": "0.0.9",
+  "version": "1.0.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "ts-injex",
-      "version": "0.0.9",
+      "version": "1.0.0",
       "license": "MIT",
       "dependencies": {
         "eslint-plugin-prettier": "^5.2.1",
         "jest-environment-jsdom": "^29.7.0"
       },
+      "bin": {
+        "tsinjex-generate": "bin/generate-imports.cjs"
+      },
       "devDependencies": {
         "@stylistic/eslint-plugin": "^2.6.2",
         "@types/jest": "^29.5.12",

package.json

@@ -1,10 +1,13 @@
 {
   "name": "ts-injex",
-  "version": "0.0.12",
+  "version": "1.1.0",
   "description": "Simple boilerplate code free dependency injection system for TypeScript.",
   "type": "module",
   "main": "./dist/index.js",
   "types": "./dist/index.d.ts",
+  "bin": {
+    "tsinjex-generate": "./bin/generate-imports.cjs"
+  },
   "scripts": {
     "prepare": "npm run build",
     "build": "npm run build:tsc",
@@ -22,7 +25,8 @@
     "docs:fix:coverage": "node scripts/fix-coverage-paths.cjs",
     "docs:generate:badge": "node scripts/generate-badge.cjs",
     "docs:fix:escape": "node scripts/replace-doc-escaping.cjs",
-    "version:show": "node -e \"console.log(require('./package.json').version)\""
+    "version:show": "node -e \"console.log(require('./package.json').version)\"",
+    "prepare:deploy": "npm install && npm run test:verbose && npm run build:tsc"
   },
   "repository": {
     "type": "git",

src/__tests__/Decorators.spec.ts

@@ -1,8 +1,9 @@
+/* istanbul ignore file */
 /* eslint-disable @typescript-eslint/no-explicit-any */
-import { Inject } from 'src/decorators/Inject';
-import { DependencyResolutionError } from 'src/interfaces/Exceptions';
-import { ForceConstructor } from 'src/types/GenericContructor';
-import { ITSinjex_, ITSinjex } from '../interfaces/ITSinjex';
+import { Inject } from '../decorators/Inject.js';
+import { DependencyResolutionError } from '../interfaces/Exceptions.js';
+import { ITSinjex_, ITSinjex } from '../interfaces/ITSinjex.js';
+import { ForceConstructor } from '../types/GenericContructor.js';
 
 /**
  * Test the Inject decorator.
@@ -117,6 +118,130 @@ export function test_InjectDecorator(
             }
             expect(_error).toBeInstanceOf(DependencyResolutionError);
         });
+
+        it('should replace the property with the resolved dependency', () => {
+            container.register('MockDependencyIdentifier', {
+                value: 'test-value',
+            });
+
+            class TestClass {
+                @Inject('MockDependencyIdentifier')
+                private readonly _dependency!: any;
+
+                public getDependency() {
+                    return this._dependency;
+                }
+
+                public isDependencyTypeofFunction() {
+                    return typeof this._dependency === 'function';
+                }
+            }
+
+            const instance = new TestClass();
+
+            expect(instance.getDependency().value).toBe('test-value');
+
+            expect(instance.isDependencyTypeofFunction()).toBe(false);
+            expect(instance.getDependency().value).toBe('test-value');
+        });
+
+        it('should use a empty initializer when none is provided but true', () => {
+            container.register(
+                'MockDependencyIdentifier',
+                class X {
+                    public value: string = 'test-value';
+                    constructor() {}
+                },
+            );
+
+            class TestClass {
+                @Inject('MockDependencyIdentifier', true)
+                private readonly _dependency!: any;
+
+                public getDependency() {
+                    return this._dependency;
+                }
+            }
+
+            const instance = new TestClass();
+            expect(instance.getDependency().value).toBe('test-value');
+        });
+
+        it('should throw an error when the dependency has no instantiation method', () => {
+            container.register('MockDependencyIdentifier', {
+                value: 'test-value',
+            });
+
+            class TestClass {
+                @Inject('MockDependencyIdentifier', true)
+                private readonly _dependency!: any;
+
+                public getDependency() {
+                    return this._dependency;
+                }
+            }
+
+            expect(() => {
+                const instance = new TestClass();
+                instance.getDependency();
+            }).toThrow(new RegExp('No instantiation method found for.*'));
+        });
+
+        it('should not throw an error when the dependency has no instantiation method if not necessary', () => {
+            container.register('MockDependencyIdentifier', {
+                value: 'test-value',
+            });
+
+            class TestClass {
+                @Inject('MockDependencyIdentifier', true, false)
+                private readonly _dependency!: any;
+
+                public getDependency() {
+                    return this._dependency;
+                }
+            }
+
+            expect(() => {
+                const instance = new TestClass();
+                instance.getDependency();
+            }).not.toThrow(new RegExp('No instantiation method found for.*'));
+        });
+
+        it('should throw an error when the dependency cannot be resolved', () => {
+            container.register('MockDependencyIdentifier', null);
+
+            class TestClass {
+                @Inject('MockDependencyIdentifier', true)
+                private readonly _dependency!: any;
+
+                public getDependency() {
+                    return this._dependency;
+                }
+            }
+
+            expect(() => {
+                const instance = new TestClass();
+                instance.getDependency();
+            }).toThrow(new RegExp('.*could not be resolved.*'));
+        });
+
+        it('should not throw an error when the dependency cannot be resolved if not necessary', () => {
+            container.register('MockDependencyIdentifier', null);
+
+            class TestClass {
+                @Inject('MockDependencyIdentifier', true, false)
+                private readonly _dependency!: any;
+
+                public getDependency() {
+                    return this._dependency;
+                }
+            }
+
+            expect(() => {
+                const instance = new TestClass();
+                instance.getDependency();
+            }).not.toThrow(new RegExp('.*could not be resolved.*'));
+        });
     });
 }
 
@@ -157,6 +282,7 @@ export function test_RegisterInstanceDecorator(
     Container: ITSinjex_,
     // eslint-disable-next-line @typescript-eslint/no-unsafe-function-type
     registerInstance: Function,
+    mode: 'instance' | 'standalone' = 'standalone',
 ): void {
     describe('RegisterInstance Decorator Tests', () => {
         let container: ITSinjex;
@@ -170,7 +296,10 @@ export function test_RegisterInstanceDecorator(
         });
 
         it('should register an instance of a dependency', () => {
-            @registerInstance('InstanceIdentifier')
+            @registerInstance(
+                'InstanceIdentifier',
+                mode === 'instance' ? 'instance' : undefined,
+            )
             class TestClass {
                 private readonly _dependency!: any;
 
@@ -212,7 +341,10 @@ export function test_RegisterInstanceDecorator(
         });
 
         it('should register an instance of a dependency and get it on set', () => {
-            @registerInstance('InstanceIdentifier')
+            @registerInstance(
+                'InstanceIdentifier',
+                mode === 'instance' ? 'instance' : undefined,
+            )
             class TestClass {
                 private readonly _dependency!: any;
 

src/__tests__/Decorators.test.ts

@@ -1,15 +1,18 @@
-import { TSinjex } from 'src/classes/TSinjex';
-import { Inject } from 'src/decorators/Inject';
-import { Register } from 'src/decorators/Register';
-import { RegisterInstance } from 'src/decorators/RegisterInstance';
+/* eslint-disable deprecation/deprecation */
+import { TSinjex } from 'src/classes/TSinjex.js';
+import { Inject } from 'src/decorators/Inject.js';
+import { Register } from 'src/decorators/Register.js';
+import { RegisterInstance } from 'src/decorators/RegisterInstance.js';
 import {
     test_InjectDecorator,
     test_RegisterDecorator,
     test_RegisterInstanceDecorator,
-} from './Decorators.spec';
+} from './Decorators.spec.js';
 
 test_InjectDecorator(TSinjex, Inject);
 
 test_RegisterDecorator(TSinjex, Register);
 
 test_RegisterInstanceDecorator(TSinjex, RegisterInstance);
+
+test_RegisterInstanceDecorator(TSinjex, Register, 'instance');

src/__tests__/Functions.spec.ts

@@ -1,5 +1,11 @@
+/* istanbul ignore file */
 /* eslint-disable @typescript-eslint/no-explicit-any */
-import { ITSinjex, ITSinjex_ } from 'src/interfaces/ITSinjex';
+import {
+    DependencyResolutionError,
+    InitializationError,
+    NoInstantiationMethodError,
+} from '../interfaces/Exceptions.js';
+import { ITSinjex, ITSinjex_ } from '../interfaces/ITSinjex.js';
 
 export function test_RegisterFunction(
     Container: ITSinjex_,
@@ -68,3 +74,111 @@ export function test_ResolveFunction(
         });
     });
 }
+
+/**
+ * Test the inject function.
+ * @param Container The DI container implementation to test against.
+ * @param inject The inject function to test.
+ */
+export function test_injectFunction(
+    Container: ITSinjex_,
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-function-type
+    inject: Function,
+): void {
+    describe('inject Function Tests', () => {
+        let container: ITSinjex;
+
+        beforeEach(() => {
+            // Reset singleton
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+            (Container as any)['_instance'] = undefined;
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+            (Container as any)['_dependencies'] = undefined;
+            container = Container.getInstance();
+        });
+
+        it('should resolve and return the dependency as is', () => {
+            container.register('SimpleDep', { value: 'test' });
+
+            const resolved = inject('SimpleDep');
+            expect(resolved.value).toBe('test');
+        });
+
+        it('should resolve and run the initializer function', () => {
+            container.register('DepWithInit', { value: 'before' });
+
+            const resolved = inject('DepWithInit', (dep: any) => {
+                dep.value = 'after';
+
+                return dep;
+            });
+
+            expect(resolved.value).toBe('after');
+        });
+
+        it('should resolve and instantiate the dependency if init is true and constructor exists', () => {
+            class WithConstructor {
+                value = 'constructed';
+            }
+
+            container.register('Constructable', WithConstructor);
+
+            const resolved = inject('Constructable', true);
+            expect(resolved.value).toBe('constructed');
+        });
+
+        it('should return undefined if dependency is not found and not necessary', () => {
+            const resolved = inject('NonExistentDep', undefined, false);
+            expect(resolved).toBeUndefined();
+        });
+
+        it('should throw DependencyResolutionError if dependency is not found and necessary', () => {
+            expect(() => inject('MissingDep')).toThrow(
+                DependencyResolutionError,
+            );
+        });
+
+        it('should throw InitializationError if init function throws', () => {
+            container.register('InitThrows', {});
+
+            expect(() =>
+                inject('InitThrows', () => {
+                    throw new Error('fail');
+                }),
+            ).toThrow(InitializationError);
+        });
+
+        it('should throw NoInstantiationMethodError if init = true and no constructor exists', () => {
+            container.register('NonConstructable', {});
+
+            expect(() => inject('NonConstructable', true)).toThrow(
+                NoInstantiationMethodError,
+            );
+        });
+
+        it('should not throw if no constructor and necessary = false', () => {
+            container.register('SafeSkip', {});
+            expect(() => inject('SafeSkip', true, false)).not.toThrow();
+        });
+
+        it('should return undefined if initializer fails and not necessary', () => {
+            container.register('InitErrorOptional', {});
+
+            const result = inject(
+                'InitErrorOptional',
+                () => {
+                    throw new Error('ignored');
+                },
+                false,
+            );
+
+            expect(result).toBeUndefined();
+        });
+
+        it('should return undefined if dependency is null and not necessary', () => {
+            container.register('NullDep', null);
+            const result = inject('NullDep', true, false);
+            expect(result).toBeUndefined();
+        });
+    });
+}

src/__tests__/Functions.test.ts

@@ -1,7 +1,13 @@
-import { TSinjex } from 'src/classes/TSinjex';
-import { register } from 'src/functions/register';
-import { resolve } from 'src/functions/resolve';
-import { test_RegisterFunction, test_ResolveFunction } from './Functions.spec';
+import {
+    test_injectFunction,
+    test_RegisterFunction,
+    test_ResolveFunction,
+} from './Functions.spec.js';
+import { TSinjex } from '../classes/TSinjex.js';
+import { inject } from '../functions/inject.js';
+import { register } from '../functions/register.js';
+import { resolve } from '../functions/resolve.js';
 
 test_RegisterFunction(TSinjex, register);
 test_ResolveFunction(TSinjex, resolve);
+test_injectFunction(TSinjex, inject);

src/__tests__/ITSinjex.spec.ts

@@ -1,4 +1,5 @@
-import { ITSinjex_, ITSinjex } from '../interfaces/ITSinjex';
+/* istanbul ignore file */
+import { ITSinjex_, ITSinjex } from '../interfaces/ITSinjex.js';
 
 /**
  * Test the implementation of the `ITSinjex` interface.

src/__tests__/TSinjex.test.ts

@@ -1,4 +1,4 @@
-import { test_ITSinjex } from './ITSinjex.spec';
-import { TSinjex } from '../classes/TSinjex';
+import { test_ITSinjex } from './ITSinjex.spec.js';
+import { TSinjex } from '../classes/TSinjex.js';
 
 test_ITSinjex(TSinjex);

src/classes/TSinjex.ts

@@ -1,13 +1,13 @@
-import { Identifier } from 'src/types/Identifier';
-import type { Inject } from '../decorators/Inject';
-import type { Register } from '../decorators/Register';
-import type { RegisterInstance } from '../decorators/RegisterInstance';
-import type { register } from '../functions/register';
-import type { resolve } from '../functions/resolve';
-import { ImplementsStatic } from '../helper/ImplementsStatic';
-import { DependencyResolutionError } from '../interfaces/Exceptions';
-import { IDependency } from '../interfaces/IDependency';
-import { ITSinjex, ITSinjex_ } from '../interfaces/ITSinjex';
+import type { Inject } from '../decorators/Inject.js';
+import type { Register } from '../decorators/Register.js';
+import type { RegisterInstance } from '../decorators/RegisterInstance.js';
+import type { register } from '../functions/register.js';
+import type { resolve } from '../functions/resolve.js';
+import { ImplementsStatic } from '../helper/ImplementsStatic.js';
+import { DependencyResolutionError } from '../interfaces/Exceptions.js';
+import { IDependency } from '../interfaces/IDependency.js';
+import { ITSinjex, ITSinjex_ } from '../interfaces/ITSinjex.js';
+import { Identifier } from '../types/Identifier.js';
 
 /**
  * # TSinjex
@@ -114,7 +114,7 @@ export class TSinjex implements ITSinjex {
         }
 
         if (dependency.deprecated) {
-            console.warn(`Dependency ${identifier} is deprecated`);
+            console.warn(`Dependency ${identifier.toString()} is deprecated`);
 
             // Remove the deprecation warning; it should only be logged once.
             dependency.deprecated = false;

src/decorators/Inject.ts

@@ -1,6 +1,12 @@
-import { Identifier } from 'src/types/Identifier';
-import { TSinjex } from '../classes/TSinjex';
-import { InitDelegate } from '../types/InitDelegate';
+import { TSinjex } from '../classes/TSinjex.js';
+import {
+    DependencyResolutionError,
+    InitializationError,
+    InjectorError,
+    NoInstantiationMethodError,
+} from '../interfaces/Exceptions.js';
+import { Identifier } from '../types/Identifier.js';
+import { InitDelegate } from '../types/InitDelegate.js';
 
 /**
  * A decorator to inject a dependency from a DI (Dependency Injection) container into a class property.
@@ -8,12 +14,17 @@ import { InitDelegate } from '../types/InitDelegate';
  * @template U The type of the property to be injected.
  * @param identifier The identifier used to resolve the class in the DI container.
  * @see {@link Identifier} for more information on identifiers.
- * @param init An optional initializer function to transform the dependency before injection.
+ * @param init Optional an initializer function to transform the dependency before injection
+ * or true to instantiate the dependency if it has a constructor.
  * @see {@link InitDelegate} for more information on initializer functions.
- * @param necessary If true, throws an error if the dependency is not found.
+ * @param isNecessary If true, throws an error if the dependency is not found.
  * @returns The resolved dependency or undefined if the dependency is not necessary
  * and not found, or throws an error if the dependency is necessary and not found.
- * @throws A {@link DependencyResolutionError} if the dependency is not found and necessary.
+ * @throws **Only throws errors if the dependency is necessary.**
+ * @throws A {@link DependencyResolutionError} if the dependency is not found.
+ * @throws A {@link InjectorError} if an error occurs during the injection process.
+ * @throws A {@link NoInstantiationMethodError} if the dependency does not have a constructor.
+ * @throws An {@link InitializationError} if an error occurs during the initialization process.
  * @example
  * ```ts
  * class MyClass {
@@ -31,47 +42,110 @@ import { InitDelegate } from '../types/InitDelegate';
  */
 export function Inject<T, U>(
     identifier: Identifier,
-    init?: InitDelegate<T, U>,
-    necessary = true,
+    init?: InitDelegate<T, U> | true,
+    isNecessary = true,
 ) {
     return function (target: unknown, propertyKey: string | symbol): void {
-        // Unique symbol to store the private property
-        const privatePropertyKey: unique symbol = Symbol();
-        // Get the DI container instance
-        const diContainer = TSinjex.getInstance();
-
-        // Function to evaluate the dependency lazily
-        // to avoid circular dependencies, not found dependencies, etc.
-        const evaluate = (): T | undefined => {
-            return diContainer.resolve<T>(identifier, necessary);
+        /**
+         * Function to evaluate the dependency lazily
+         * to avoid circular dependencies, not found dependencies, etc.
+         * @returns The resolved dependency or undefined if the dependency is not found.
+         */
+        const resolve = (): T | undefined => {
+            return TSinjex.getInstance().resolve<T>(identifier, isNecessary);
         };
 
-        // Define the property
         Object.defineProperty(target, propertyKey, {
             get() {
-                // If the property is not defined, evaluate the dependency
-                if (!this.hasOwnProperty(privatePropertyKey)) {
-                    if (init) {
-                        try {
-                            this[privatePropertyKey] = init(evaluate() as T);
-                        } catch (error) {
-                            if (necessary) {
-                                throw error;
-                            }
-                        }
-                    } else {
-                        this[privatePropertyKey] = evaluate();
-                    }
-                }
+                let instance: T | U | undefined;
 
-                return this[privatePropertyKey];
+                const dependency: T | undefined = tryAndCatch(
+                    () => resolve(),
+                    isNecessary,
+                    identifier,
+                    DependencyResolutionError,
+                );
+
+                if (dependency != null) {
+                    const initFunction: (() => U) | undefined =
+                        typeof init === 'function' && dependency != null
+                            ? (): U => init(dependency)
+                            : init === true && hasConstructor(dependency)
+                              ? (): U => new dependency() as U
+                              : undefined;
+
+                    if (init == null) instance = dependency;
+                    else if (initFunction != null)
+                        instance = tryAndCatch(
+                            initFunction,
+                            isNecessary,
+                            identifier,
+                            InitializationError,
+                        );
+                    else if (isNecessary)
+                        throw new NoInstantiationMethodError(identifier);
+                } else if (isNecessary)
+                    throw new DependencyResolutionError(identifier);
+
+                /**
+                 * Replace itself with the resolved dependency
+                 * for performance reasons.
+                 */
+                Object.defineProperty(this, propertyKey, {
+                    value: instance,
+                    writable: false,
+                    enumerable: false,
+                    configurable: false,
+                });
+
+                return instance;
             },
-            // Not necessary to set the property
-            // set(value: PropertieType) {
-            //     this[privatePropertyKey] = value;
-            // },
-            enumerable: true,
-            configurable: false,
+            /**
+             * Make the property configurable to allow replacing it
+             */
+            configurable: true,
         });
     };
 }
+
+/**
+ * Tries to execute a function and catches any errors that occur.
+ * If the function is necessary and an error occurs, it throws the error
+ * with the specified error class and identifier.
+ * @param fn The function to execute.
+ * @param necessary If true, throws an error if an error occurs.
+ * @param identifier The identifier of the dependency.
+ * @param errorClass The error class to throw if an error occurs.
+ * @returns The result of the function or undefined if an error occurs and the function is not necessary.
+ */
+function tryAndCatch<ReturnType, ErrorType>(
+    fn: () => ReturnType,
+    necessary: boolean,
+    identifier?: Identifier,
+    errorClass?: ErrorType,
+): ReturnType | undefined {
+    try {
+        return fn();
+    } catch (error) {
+        if (necessary)
+            throw new (errorClass != null ? errorClass : error)(
+                identifier ?? 'not specified',
+                error,
+            );
+        else return undefined;
+    }
+}
+
+/**
+ * Checks if an object has a constructor.
+ * @param obj The object to check.
+ * @returns True if the object has a constructor, false otherwise.
+ */
+function hasConstructor<T>(obj: T): obj is T & { new (): unknown } {
+    const _obj = obj as unknown as { prototype?: { constructor?: unknown } };
+
+    return (
+        _obj?.prototype != null &&
+        typeof _obj.prototype.constructor === 'function'
+    );
+}

src/decorators/Register.ts

@@ -1,5 +1,133 @@
-import { Identifier } from 'src/types/Identifier';
-import { TSinjex } from '../classes/TSinjex';
+import { InitDelegate } from 'src/types/InitDelegate.js';
+import { TSinjex } from '../classes/TSinjex.js';
+import { Identifier } from '../types/Identifier.js';
+
+//#region Overloads
+
+/**
+ * A decorator to register a class in the **TSinjex** DI (Dependency Injection) container.
+ * @template TargetType The type of the class to be registered.
+ * @param identifier The identifier used to register the class in the DI container.
+ * @see {@link Identifier} for more information on identifiers.
+ * @param deprecated If true, the dependency is deprecated and a warning
+ * is logged only once upon the first resolution of the dependency.
+ * @returns The decorator function to be applied on the class.
+ * @example
+ * ```ts
+ * \@Register('MyClassIdentifier')
+ * class MyClass {
+ *   // ...
+ * }
+ * ```
+ * @example
+ * ```ts
+ * \@Register('MyClassIdentifier', true)
+ * class MyClass {
+ *   // ...
+ * }
+ * ```
+ */
+export function Register<
+    TargetType extends new (...args: unknown[]) => InstanceType<TargetType>,
+>(
+    identifier: Identifier,
+    deprecated?: boolean,
+): (constructor: TargetType, ...args: unknown[]) => void;
+
+/**
+ * A decorator to register an instance of a class in the DI (Dependency Injection) container.
+ * @template TargetType The type of the class whose instance is to be registered.
+ * @param identifier The identifier used to register the instance in the DI container.
+ * @see {@link Identifier} for more information on identifiers.
+ * @param shouldRegister Set to 'instance' to register the instance in the DI container
+ * with an empty constructor.
+ * @param deprecated If true, the dependency is deprecated and a warning
+ * is logged only once upon the first resolution of the dependency.
+ * @returns The decorator function to be applied on the class.
+ * @example
+ * ```ts
+ * \@RegisterInstance('MyClassInstanceIdentifier', 'instance')
+ * class MyClass {
+ *   // ...
+ * }
+ * ```
+ * @example
+ * ```ts
+ * \@RegisterInstance('MyClassInstanceIdentifier', 'instance', true)
+ * class MyClass {
+ *   // ...
+ * }
+ * ```
+ */
+export function Register<
+    TargetType extends new (..._args: unknown[]) => InstanceType<TargetType>,
+>(
+    identifier: Identifier,
+    shouldRegister: 'instance',
+    deprecated?: boolean,
+): (constructor: TargetType, ...args: unknown[]) => void;
+
+/**
+ * A decorator to register an instance of a class in the DI (Dependency Injection) container.
+ * @template TargetType The type of the class whose instance is to be registered.
+ * @param identifier The identifier used to register the instance in the DI container.
+ * @see {@link Identifier} for more information on identifiers.
+ * @param init An optional initializer function which get the constructor of the class
+ * as input and returns an instance of the class.
+ * @param deprecated If true, the dependency is deprecated and a warning
+ * is logged only once upon the first resolution of the dependency.
+ * @see {@link InitDelegate} for more information on initializer functions.
+ * @returns The decorator function to be applied on the class.
+ * @example
+ * ```ts
+ * \@RegisterInstance('MyClassInstanceIdentifier', (constructor) => new constructor())
+ * class MyClass {
+ *   // ...
+ * }
+ * ```
+ * @example
+ * ```ts
+ * \@RegisterInstance('MyClassInstanceIdentifier', (constructor) => new constructor(), true)
+ * class MyClass {
+ *   // ...
+ * }
+ * ```
+ */
+export function Register<
+    TargetType extends new (..._args: unknown[]) => InstanceType<TargetType>,
+>(
+    identifier: Identifier,
+    init?: InitDelegate<
+        TargetType & { new (..._args: unknown[]): InstanceType<TargetType> },
+        InstanceType<TargetType>
+    >,
+    deprecated?: boolean,
+): (constructor: TargetType, ...args: unknown[]) => void;
+
+//#endregion Overloads
+
+// eslint-disable-next-line jsdoc/require-jsdoc
+export function Register<
+    TargetType extends new (...args: unknown[]) => InstanceType<TargetType>,
+>(
+    identifier: Identifier,
+    arg1?:
+        | undefined
+        | boolean
+        | InitDelegate<TargetType, InstanceType<TargetType>>
+        | 'instance',
+    arg2?: boolean,
+): (constructor: TargetType, ...args: unknown[]) => void {
+    const deprecated = typeof arg1 === 'boolean' ? arg1 : arg2;
+    const init = typeof arg1 === 'function' ? arg1 : undefined;
+    const shouldRegisterInstance = arg1 === 'instance';
+
+    if (init == undefined && shouldRegisterInstance !== true) {
+        return _register(identifier, deprecated);
+    } else {
+        return _registerInstance(identifier, init, deprecated);
+    }
+}
 
 /**
  * A decorator to register a class in the **TSinjex** DI (Dependency Injection) container.
@@ -17,7 +145,7 @@ import { TSinjex } from '../classes/TSinjex';
  * }
  * ```
  */
-export function Register<
+function _register<
     TargetType extends new (...args: unknown[]) => InstanceType<TargetType>,
 >(identifier: Identifier, deprecated?: boolean) {
     return function (constructor: TargetType, ...args: unknown[]): void {
@@ -28,3 +156,111 @@ export function Register<
         diContainer.register(identifier, constructor, deprecated);
     };
 }
+
+/**
+ * A decorator to register an instance of a class in the DI (Dependency Injection) container.
+ * @template TargetType The type of the class whose instance is to be registered.
+ * @param identifier The identifier used to register the instance in the DI container.
+ * @see {@link Identifier} for more information on identifiers.
+ * @param init An optional initializer function which get the constructor of the class
+ * as input and returns an instance of the class.
+ * @param deprecated If true, the dependency is deprecated and a warning
+ * is logged only once upon the first resolution of the dependency.
+ * @see {@link InitDelegate} for more information on initializer functions.
+ * @returns The decorator function to be applied on the class.
+ * @example
+ * ```ts
+ * \@RegisterInstance('MyClassInstanceIdentifier', (constructor) => new constructor())
+ * class MyClass {
+ *   // ...
+ * }
+ * ```
+ */
+function _registerInstance<
+    TargetType extends new (..._args: unknown[]) => InstanceType<TargetType>,
+>(
+    identifier: Identifier,
+    init?: InitDelegate<
+        TargetType & { new (..._args: unknown[]): InstanceType<TargetType> },
+        InstanceType<TargetType>
+    >,
+    deprecated?: boolean,
+) {
+    return function (constructor: TargetType, ...args: unknown[]): void {
+        // Get the instance of the DI container
+        const diContainer = TSinjex.getInstance();
+        let instance: InstanceType<TargetType>;
+
+        // Create a proxy to instantiate the class when needed (Lazy Initialization)
+        let lazyProxy: unknown = new Proxy(
+            {},
+            {
+                get(target, prop, receiver) {
+                    ({ instance, lazyProxy } = initializeInstance<TargetType>(
+                        instance,
+                        init,
+                        constructor,
+                        args,
+                        lazyProxy,
+                    ));
+
+                    // Return the requested property of the instance
+                    return instance[prop as keyof InstanceType<TargetType>];
+                },
+                set(target, prop, value, receiver) {
+                    ({ instance, lazyProxy } = initializeInstance<TargetType>(
+                        instance,
+                        init,
+                        constructor,
+                        args,
+                        lazyProxy,
+                    ));
+
+                    // Set the requested property of the instance
+                    return (instance[prop as keyof InstanceType<TargetType>] =
+                        value);
+                },
+            },
+        );
+
+        // Register the lazy proxy in the DI container
+        diContainer.register(identifier, lazyProxy, deprecated);
+    };
+}
+
+/**
+ * Initializes the instance of the class.
+ * @template TargetType The type of the class whose instance is to be initialized.
+ * @param instance The instance of the class to be initialized.
+ * @param init The optional initializer function to initialize the instance.
+ * @param constructor The constructor of the class.
+ * @param args The arguments to be passed to the constructor of the class.
+ * @param lazyProxy The lazy proxy to instantiate the class when needed.
+ * @returns The initialized instance and the lazy proxy.
+ */
+function initializeInstance<
+    TargetType extends new (..._args: unknown[]) => InstanceType<TargetType>,
+>(
+    instance: InstanceType<TargetType>,
+    init:
+        | InitDelegate<
+              TargetType &
+                  (new (..._args: unknown[]) => InstanceType<TargetType>),
+              InstanceType<TargetType>
+          >
+        | undefined,
+    constructor: TargetType,
+    args: unknown[],
+    lazyProxy: unknown,
+): { instance: InstanceType<TargetType>; lazyProxy: unknown } {
+    if (instance == null) {
+        if (init) {
+            instance = init(constructor);
+        } else {
+            instance = new constructor(...args);
+        }
+    }
+    lazyProxy = instance;
+
+    return { instance, lazyProxy };
+}

src/decorators/RegisterInstance.ts

@@ -1,6 +1,6 @@
-import { Identifier } from 'src/types/Identifier';
-import { TSinjex } from '../classes/TSinjex';
-import { InitDelegate } from '../types/InitDelegate';
+import { Register } from './Register.js';
+import { Identifier } from '../types/Identifier.js';
+import { InitDelegate } from '../types/InitDelegate.js';
 
 /**
  * A decorator to register an instance of a class in the DI (Dependency Injection) container.
@@ -9,6 +9,8 @@ import { InitDelegate } from '../types/InitDelegate';
  * @see {@link Identifier} for more information on identifiers.
  * @param init An optional initializer function which get the constructor of the class
  * as input and returns an instance of the class.
+ * @param deprecated If true, the dependency is deprecated and a warning
+ * is logged only once upon the first resolution of the dependency.
  * @see {@link InitDelegate} for more information on initializer functions.
  * @returns The decorator function to be applied on the class.
  * @example
@@ -18,6 +20,7 @@ import { InitDelegate } from '../types/InitDelegate';
  *   // ...
  * }
  * ```
+ * @deprecated Use {@link Register} instead. This decorator already uses the {@link Register} decorator internally.
  */
 export function RegisterInstance<
     TargetType extends new (..._args: unknown[]) => InstanceType<TargetType>,
@@ -27,47 +30,10 @@ export function RegisterInstance<
         TargetType & { new (..._args: unknown[]): InstanceType<TargetType> },
         InstanceType<TargetType>
     >,
-) {
-    return function (constructor: TargetType, ...args: unknown[]): void {
-        // Get the instance of the DI container
-        const diContainer = TSinjex.getInstance();
-        let instance: InstanceType<TargetType>;
+    deprecated?: boolean,
+): (constructor: TargetType, ...args: unknown[]) => void {
+    const initDelegate = typeof init === 'function' ? init : undefined;
 
-        // Create a proxy to instantiate the class when needed (Lazy Initialization)
-        let lazyProxy: unknown = new Proxy(
-            {},
-            {
-                get(target, prop, receiver) {
-                    if (instance == null) {
-                        if (init) {
-                            instance = init(constructor);
-                        } else {
-                            instance = new constructor(...args);
-                        }
-                    }
-                    lazyProxy = instance;
-
-                    // Return the requested property of the instance
-                    return instance[prop as keyof InstanceType<TargetType>];
-                },
-                set(target, prop, value, receiver) {
-                    if (instance == null) {
-                        if (init) {
-                            instance = init(constructor);
-                        } else {
-                            instance = new constructor(...args);
-                        }
-                    }
-                    lazyProxy = instance;
-
-                    // Set the requested property of the instance
-                    return (instance[prop as keyof InstanceType<TargetType>] =
-                        value);
-                },
-            },
-        );
-
-        // Register the lazy proxy in the DI container
-        diContainer.register(identifier, lazyProxy);
-    };
+    if (initDelegate) return Register(identifier, initDelegate, deprecated);
+    else return Register(identifier, 'instance', deprecated);
 }

src/functions/inject.ts

@@ -0,0 +1,113 @@
+import { TSinjex } from '../classes/TSinjex.js';
+import {
+    DependencyResolutionError,
+    InitializationError,
+    InjectorError,
+    NoInstantiationMethodError,
+} from '../interfaces/Exceptions.js';
+import { Identifier } from '../types/Identifier.js';
+import { InitDelegate } from '../types/InitDelegate.js';
+
+/**
+ * A function to inject a dependency from a DI (Dependency Injection) container into a variable.
+ * @template T The type of the dependency to be injected.
+ * @template U The type of the property to be injected.
+ * @param identifier The identifier used to resolve the class in the DI container.
+ * @see {@link Identifier} for more information on identifiers.
+ * @param init Optional an initializer function to transform the dependency before injection
+ * or true to instantiate the dependency if it has a constructor.
+ * @see {@link InitDelegate} for more information on initializer functions.
+ * @param isNecessary If true, throws an error if the dependency is not found.
+ * @returns The resolved dependency or undefined if the dependency is not necessary
+ * and not found, or throws an error if the dependency is necessary and not found.
+ * @throws **Only throws errors if the dependency is necessary.**
+ * @throws A {@link DependencyResolutionError} if the dependency is not found.
+ * @throws A {@link InjectorError} if an error occurs during the injection process.
+ * @throws A {@link NoInstantiationMethodError} if the dependency does not have a constructor.
+ * @throws An {@link InitializationError} if an error occurs during the initialization process.
+ * @example
+ * ```ts
+ * let myDependency = inject<MyDependency>('MyDependencyIdentifier');
+ * ```
+ * @example
+ * ```ts
+ * let logger = inject<ILogger>('ILogger_', (x: ILogger_) => x.getLogger('Tags'), false);
+ * ```
+ */
+export function inject<T, U>(
+    identifier: Identifier,
+    init?: InitDelegate<T, U> | true,
+    isNecessary = true,
+): T | U | undefined {
+    let instance: T | U | undefined;
+
+    const dependency: T | undefined = tryAndCatch(
+        () => TSinjex.getInstance().resolve<T>(identifier, isNecessary),
+        isNecessary,
+        identifier,
+        DependencyResolutionError,
+    );
+
+    if (dependency != null) {
+        const initFunction: (() => U) | undefined =
+            typeof init === 'function' && dependency != null
+                ? (): U => init(dependency)
+                : init === true && hasConstructor(dependency)
+                  ? (): U => new dependency() as U
+                  : undefined;
+
+        if (init == null) instance = dependency;
+        else if (initFunction != null)
+            instance = tryAndCatch(
+                initFunction,
+                isNecessary,
+                identifier,
+                InitializationError,
+            );
+        else if (isNecessary) throw new NoInstantiationMethodError(identifier);
+    } else if (isNecessary) throw new DependencyResolutionError(identifier);
+
+    return instance as T | U;
+}
+
+/**
+ * Tries to execute a function and catches any errors that occur.
+ * If the function is necessary and an error occurs, it throws the error
+ * with the specified error class and identifier.
+ * @param fn The function to execute.
+ * @param necessary If true, throws an error if an error occurs.
+ * @param identifier The identifier of the dependency.
+ * @param errorClass The error class to throw if an error occurs.
+ * @returns The result of the function or undefined if an error occurs and the function is not necessary.
+ */
+function tryAndCatch<ReturnType, ErrorType>(
+    fn: () => ReturnType,
+    necessary: boolean,
+    identifier?: Identifier,
+    errorClass?: ErrorType,
+): ReturnType | undefined {
+    try {
+        return fn();
+    } catch (error) {
+        if (necessary)
+            throw new (errorClass != null ? errorClass : error)(
+                identifier ?? 'not specified',
+                error,
+            );
+        else return undefined;
+    }
+}
+
+/**
+ * Checks if an object has a constructor.
+ * @param obj The object to check.
+ * @returns True if the object has a constructor, false otherwise.
+ */
+function hasConstructor<T>(obj: T): obj is T & { new (): unknown } {
+    const _obj = obj as unknown as { prototype?: { constructor?: unknown } };
+
+    return (
+        _obj?.prototype != null &&
+        typeof _obj.prototype.constructor === 'function'
+    );
+}

src/functions/register.ts

@@ -1,5 +1,5 @@
-import { Identifier } from 'src/types/Identifier';
-import { TSinjex } from '../classes/TSinjex';
+import { TSinjex } from '../classes/TSinjex.js';
+import { Identifier } from '../types/Identifier.js';
 
 /**
  * Register a dependency.

src/functions/resolve.ts

@@ -1,6 +1,6 @@
-import { Identifier } from 'src/types/Identifier';
-import { TSinjex } from '../classes/TSinjex';
-import { DependencyResolutionError } from '../interfaces/Exceptions';
+import { TSinjex } from '../classes/TSinjex.js';
+import { DependencyResolutionError } from '../interfaces/Exceptions.js';
+import { Identifier } from '../types/Identifier.js';
 
 /**
  * Resolve a dependency.
@@ -15,12 +15,12 @@ export function resolve<T>(identifier: Identifier): T;
  * Resolve a dependency
  * @param identifier The identifier used to register the class in the DI container.
  * @see {@link Identifier} for more information on identifiers.
- * @param necessary The dependency is **not** necessary.
+ * @param isNecessary The dependency is **not** necessary.
  * @returns The resolved dependency or undefined if the dependency is not found.
  */
 export function resolve<T>(
     identifier: Identifier,
-    necessary: false,
+    isNecessary: false,
 ): T | undefined;
 
 /**

src/index.ts

@@ -1,18 +1,22 @@
 /* istanbul ignore file */
 
 // Main
-export * from './classes/TSinjex';
+export * from './classes/TSinjex.js';
 
 // Decorators
-export * from './decorators/Inject';
-export * from './decorators/Register';
-export * from './decorators/RegisterInstance';
+export * from './decorators/Inject.js';
+export * from './decorators/Register.js';
+export * from './decorators/RegisterInstance.js';
+
+// Helper
+export * from './helper/ImplementsStatic.js';
 
 // Functions
-export * from './functions/resolve';
-export * from './functions/register';
+export * from './functions/resolve.js';
+export * from './functions/register.js';
+export * from './functions/inject.js';
 
 // Interfaces & Types
-export type * from './interfaces/ITSinjex';
-export type * from './types/InitDelegate';
-export type * from './types/GenericContructor';
+export type * from './interfaces/ITSinjex.js';
+export type * from './types/InitDelegate.js';
+export type * from './types/GenericContructor.js';

src/interfaces/Exceptions.ts

@@ -1,4 +1,5 @@
-import { ITSinjex } from './ITSinjex';
+import { Identifier } from 'src/types/Identifier.js';
+import { ITSinjex } from './ITSinjex.js';
 
 /**
  * General error class for {@link ITSinjex} interface.
@@ -23,8 +24,61 @@ export class DependencyResolutionError extends TSinjexError {
      * Creates a new instance of {@link DependencyResolutionError}
      * @param identifier **The identifier of the dependency**
      */
-    constructor(identifier: string) {
-        super(`Dependency ${identifier} could not be resolved.`);
+    constructor(identifier: Identifier) {
+        super(`Dependency ${identifier.toString()} could not be resolved.`);
         this.name = 'TSinjexResolutionError';
     }
 }
+
+/**
+ * Error class for Injector errors in {@link ITSinjex}.
+ * @see {@link ITSinjex.inject}
+ */
+export class InjectorError extends TSinjexError {
+    /**
+     * Creates a new instance of {@link InjectorError}
+     * @param identifier **The identifier of the dependency**
+     * @param originalError **The original error that caused the injection error**
+     */
+    constructor(identifier: Identifier, originalError?: Error) {
+        super(
+            `Error injecting dependency ${identifier.toString()} with error: "${originalError}"`,
+        );
+        this.name = 'TSinjexInjectorError';
+    }
+}
+
+/**
+ * Error class for missing instantiation methods in {@link ITSinjex}.
+ * @see {@link ITSinjex.inject}
+ */
+export class NoInstantiationMethodError extends TSinjexError {
+    /**
+     * Creates a new instance of {@link NoInstantiationMethodError}
+     * @param identifier **The identifier of the dependency**
+     */
+    constructor(identifier: Identifier) {
+        super(
+            `No instantiation method found for dependency ${identifier.toString()}.`,
+        );
+        this.name = 'TSinjexNoInstantiationMethodError';
+    }
+}
+
+/**
+ * Error class for errors during the initialization of a dependency in {@link ITSinjex}.
+ * @see {@link ITSinjex.inject}
+ */
+export class InitializationError extends TSinjexError {
+    /**
+     * Creates a new instance of {@link InitializationError}
+     * @param identifier **The identifier of the dependency**
+     * @param originalError **The original error that caused the initialization error**
+     */
+    constructor(identifier: Identifier, originalError?: Error) {
+        super(
+            `Error initializing dependency ${identifier.toString()} with error: "${originalError}"`,
+        );
+        this.name = 'TSinjexInitializationError';
+    }
+}

src/interfaces/ITSinjex.ts

@@ -1,5 +1,5 @@
-import { Identifier } from 'src/types/Identifier';
-import { DependencyResolutionError } from './Exceptions';
+import { DependencyResolutionError } from './Exceptions.js';
+import { Identifier } from '../types/Identifier.js';
 
 /**
  * Static TSInjex Interface

src/types/Identifier.ts

@@ -8,4 +8,4 @@
  * I.e. a class `ClassA` that implements the interface `IClassA` and is
  * registered as a dependent class is registered under the interface name `IClassA`.
  */
-export type Identifier = string;
+export type Identifier = string | symbol;

tsconfig.json

@@ -7,13 +7,13 @@
         "declaration": true,
         "declarationMap": true,
         "outDir": "./dist",
-        "module": "ESNext",
-        "target": "ES6",
+        "module": "NodeNext",
+        "target": "ES2020",
         "allowJs": true,
         "noUnusedLocals": false,
         "noUnusedParameters": false,
         "noImplicitAny": true,
-        "moduleResolution": "node",
+        "moduleResolution": "NodeNext",
         "allowSyntheticDefaultImports": true,
         "importHelpers": true,
         "isolatedModules": true,