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# @loopback/tslint-config
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@loopback/tslint-config provides shared TSLint configurations to enforce consistent code style and quality standards for LoopBack TypeScript development. It offers two main configuration files: a core common configuration for essential development-time linting, and an extended build configuration that includes type-checking rules for comprehensive build-time validation.
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## Package Information
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- **Package Name**: @loopback/tslint-config
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- **Package Type**: npm
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- **Language**: TypeScript (TSLint configuration)
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- **Installation**: `npm install @loopback/tslint-config`
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## Core Imports
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This package doesn't provide programmatic imports. Instead, configurations are consumed through TSLint's `extends` mechanism:
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**Basic tslint.json:**
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```json
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{
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  "$schema": "http://json.schemastore.org/tslint",
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  "extends": ["@loopback/tslint-config/tslint.common.json"]
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}
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```
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**Build-time tslint.build.json:**
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```json
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{
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  "$schema": "http://json.schemastore.org/tslint",
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  "extends": ["@loopback/tslint-config/tslint.build.json"]
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}
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```
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## Basic Usage
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After installing the package, configure TSLint to extend the LoopBack configurations:
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**For development-time linting (editor integration):**
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```json
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{
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  "$schema": "http://json.schemastore.org/tslint",
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  "extends": ["@loopback/tslint-config/tslint.common.json"],
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  "rules": {
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    // Add any project-specific rule overrides here
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  }
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}
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```
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**For comprehensive build-time linting:**
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```json
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{
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  "$schema": "http://json.schemastore.org/tslint",
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  "extends": ["@loopback/tslint-config/tslint.build.json"],
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  "rules": {
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    // Add any project-specific rule overrides here
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  }
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}
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```
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## Capabilities
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### Common Configuration (tslint.common.json)
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Core TSLint configuration with essential rules for TypeScript development that work without type checking.
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```json { .api }
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{
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  "$schema": "http://json.schemastore.org/tslint",
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  "rulesDirectory": ["tslint-consistent-codestyle"],
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  "rules": {
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    "adjacent-overload-signatures": true,
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    "prefer-for-of": true,
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    "unified-signatures": true,
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    "no-any": true,
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    "label-position": true,
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    "no-arg": true,
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    "no-construct": true,
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    "no-duplicate-variable": true,
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    "no-invalid-this": true,
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    "no-misused-new": true,
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    "no-shadowed-variable": true,
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    "no-string-throw": true,
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    "no-unused": [true, "ignore-parameters"],
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    "no-unused-expression": true,
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    "no-var-keyword": true,
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    "triple-equals": [true, "allow-null-check", "allow-undefined-check"]
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  }
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}
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```
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**Configuration Path:** `@loopback/tslint-config/tslint.common.json`
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**Rule Categories:**
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- **TypeScript Features**: `adjacent-overload-signatures`, `prefer-for-of`, `unified-signatures`, `no-any`
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- **Error Prevention**: `label-position`, `no-arg`, `no-construct`, `no-duplicate-variable`, `no-invalid-this`, `no-misused-new`, `no-shadowed-variable`, `no-string-throw`
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- **Code Quality**: `no-unused`, `no-unused-expression`, `no-var-keyword`, `triple-equals`
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**Dependencies Required:** `tslint-consistent-codestyle` plugin for enhanced code style consistency.
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### Build Configuration (tslint.build.json)
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Extended TSLint configuration that includes all common rules plus additional type-checking rules for build-time validation.
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```json { .api }
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{
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  "$schema": "http://json.schemastore.org/tslint",
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  "extends": ["./tslint.common.json"],
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  "rules": {
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    "await-promise": [true, "PromiseLike", "RequestPromise"],
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    "no-floating-promises": [true, "PromiseLike", "RequestPromise"],
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    "no-unused-variable": false,
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    "no-void-expression": [true, "ignore-arrow-function-shorthand"]
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  }
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}
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```
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**Configuration Path:** `@loopback/tslint-config/tslint.build.json`
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**Inherits:** All rules from `tslint.common.json`
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**Additional Rules:**
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- **Promise Handling**: `await-promise`, `no-floating-promises` (supports PromiseLike and RequestPromise types)
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- **Expression Rules**: `no-void-expression` with arrow function shorthand support
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- **Rule Overrides**: Explicitly disables `no-unused-variable` in favor of the `no-unused` rule from common config
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**Use Case:** Build pipelines and comprehensive type-checking validation where full TypeScript compilation context is available.
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## Configuration Details
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### Rule Descriptions
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**TypeScript-specific rules:**
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- `adjacent-overload-signatures`: Ensures overloaded functions are grouped together
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- `prefer-for-of`: Recommends for-of loops over traditional for loops when possible
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- `unified-signatures`: Warns for overloads that could be unified into a single signature
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- `no-any`: Prohibits usage of the `any` type
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**Error prevention rules:**
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- `no-arg`: Disallows access to `arguments.callee`
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- `no-construct`: Disallows calling constructor of `String`, `Number`, and `Boolean`
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- `no-duplicate-variable`: Disallows duplicate variable declarations
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- `no-invalid-this`: Disallows using `this` in classes incorrectly
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- `no-misused-new`: Warns on apparent attempts to define constructors for interfaces
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- `no-shadowed-variable`: Disallows shadowing variable declarations
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- `no-string-throw`: Flags throwing plain strings or concatenations of strings
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- `no-unused-expression`: Disallows unused expression statements
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- `triple-equals`: Requires `===` and `!==` over `==` and `!=`
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**Build-time specific rules:**
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- `await-promise`: Warns for awaiting a value that is not a Promise
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- `no-floating-promises`: Requires Promise-returning functions to be handled appropriately
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- `no-void-expression`: Requires expressions of type void to be used in statement position
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### Dependencies
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**Runtime Dependencies:**
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```json { .api }
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{
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  "dependencies": {
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    "tslint-consistent-codestyle": "^1.14.1"
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  }
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}
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```
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**Peer Dependencies:**
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```json { .api }
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{
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  "peerDependencies": {
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    "tslint": ">=5.11.0"
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  }
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}
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```
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**Environment Requirements:**
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```json { .api }
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{
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  "engines": {
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    "node": ">=8.9"
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  }
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}
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```
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## Usage Examples
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### Basic Project Setup
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Create a `tslint.json` file in your project root:
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```json
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{
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  "$schema": "http://json.schemastore.org/tslint",
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  "extends": ["@loopback/tslint-config/tslint.common.json"],
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  "rules": {
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    // Override specific rules if needed
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    "no-console": true
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  }
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}
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```
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### Build Pipeline Integration
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Create a separate `tslint.build.json` for your build process:
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```json
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{
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  "$schema": "http://json.schemastore.org/tslint",
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  "extends": ["@loopback/tslint-config/tslint.build.json"],
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  "rules": {
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    // Build-specific overrides
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  }
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}
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```
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Then run TSLint with type checking:
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```bash
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tslint --project tsconfig.json --config tslint.build.json 'src/**/*.ts'
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```
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### IDE Integration
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Most TypeScript-enabled editors will automatically use `tslint.json` for real-time linting. The common configuration is optimized for this use case as it doesn't require type information and provides fast feedback.
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### Custom Rule Extensions
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You can extend the LoopBack configuration with your own rules:
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```json
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{
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  "$schema": "http://json.schemastore.org/tslint",
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  "extends": ["@loopback/tslint-config/tslint.common.json"],
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  "rules": {
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    // Disable a rule from the base config
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    "no-any": false,
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    // Add additional rules
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    "max-line-length": [true, 120],
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    "prefer-const": true
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  }
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}
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```