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# Code Linting
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ESLint integration with automatic configuration discovery and LoopBack-specific rules for maintaining code quality and consistency.
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## Capabilities
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### lb-eslint Command
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Runs ESLint with automatic configuration discovery and default file extensions.
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**CLI Usage:**
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```bash
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# Lint current directory
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lb-eslint .
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# Lint specific files
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lb-eslint src/index.ts src/utils.ts
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# Lint with fix
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lb-eslint --fix .
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# Report unused disable directives
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lb-eslint --report-unused-disable-directives .
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# Lint specific extensions
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lb-eslint --ext .js,.jsx,.ts,.tsx src/
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```
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**Note:** ESLint functionality is only available through the `lb-eslint` CLI command. It is not exported as a programmatic function from the main module.
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### Configuration Discovery
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Automatically discovers ESLint configuration files in the project.
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**Configuration Search Order:**
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1. `.eslintrc.js` in project root
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2. `.eslintrc.json` in project root
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3. Falls back to `@loopback/build/config/.eslintrc.js`
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**Default Configuration:**
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```javascript
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// @loopback/build/config/.eslintrc.js
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module.exports = {
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  extends: '@loopback/eslint-config',
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};
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```
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### Ignore File Support
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Automatically discovers and uses ESLint ignore files.
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```typescript { .api }
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// Automatically uses .eslintignore if present in project root
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// Falls back to @loopback/build/config/.eslintignore
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```
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**Default Ignore Patterns:**
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```
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node_modules
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dist
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```
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### File Extension Handling
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Automatically sets default file extensions if not specified.
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```typescript { .api }
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// Default extensions: .js,.ts
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// Only applied if --ext option is not provided
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```
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**Extension Examples:**
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```bash
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# Uses default extensions (.js,.ts)
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lb-eslint src/
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# Custom extensions override defaults
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lb-eslint --ext .js,.jsx,.ts,.tsx src/
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```
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### Command Line Option Passthrough
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All ESLint command line options are supported and passed through.
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```typescript { .api }
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interface ESLintOptions {
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  "--fix": boolean;                    // Automatically fix problems
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  "--fix-dry-run": boolean;           // Show fixes without applying
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  "--ext": string;                    // File extensions to lint
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  "-c" | "--config": string;          // Configuration file path
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  "--ignore-path": string;            // Ignore file path
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  "--report-unused-disable-directives": boolean; // Report unused disable comments
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  "--max-warnings": number;           // Maximum number of warnings allowed
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  "--output-file": string;            // Output file for results
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  "--format": string;                 // Output format (stylish, json, etc.)
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  "--quiet": boolean;                 // Report errors only
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  "--cache": boolean;                 // Enable result caching
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  "--cache-location": string;         // Cache file location
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}
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```
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### Integration with LoopBack ESLint Config
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Uses `@loopback/eslint-config` for consistent code style across LoopBack projects.
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**Features of @loopback/eslint-config:**
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- TypeScript support with type-aware rules
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- Consistent formatting rules aligned with Prettier
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- Best practices for Node.js and LoopBack development
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- Import/export validation
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- Accessibility rules for web components
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### Usage Examples
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**Command Line Usage:**
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```bash
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# Basic linting with default configuration
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lb-eslint .
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# Fix issues automatically
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lb-eslint --fix src/
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```
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**Package.json Integration:**
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```json
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{
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  "scripts": {
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    "lint": "lb-eslint --report-unused-disable-directives .",
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    "lint:fix": "lb-eslint --fix .",
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    "lint:check": "lb-eslint ."
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  }
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}
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```
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**Custom Configuration:**
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```bash
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# Use custom config file
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lb-eslint -c .eslintrc.custom.js src/
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# Use custom ignore file
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lb-eslint --ignore-path .eslintignore.custom src/
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# Lint specific file types
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lb-eslint --ext .ts,.d.ts src/
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```
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### Error Handling
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ESLint errors are properly propagated and handled.
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```typescript { .api }
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// Process exits with non-zero code on lint errors
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// Warnings do not cause process exit unless --max-warnings is exceeded
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// Configuration errors are reported with helpful messages
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```