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# TypeScript Libraries
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Union type defining all available TypeScript library targets for compilation and type checking. These library targets control which built-in type definitions are available during TypeScript compilation.
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## Capabilities
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### Lib Type
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Complete union type of all TypeScript library targets.
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```typescript { .api }
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type Lib =
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  // Core ECMAScript libraries
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  | 'es5'
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  | 'es6'
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  | 'es7'
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  | 'es2015'
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  | 'es2015.collection'
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  | 'es2015.core'
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  | 'es2015.generator'
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  | 'es2015.iterable'
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  | 'es2015.promise'
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  | 'es2015.proxy'
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  | 'es2015.reflect'
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  | 'es2015.symbol'
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  | 'es2015.symbol.wellknown'
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  | 'es2016'
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  | 'es2016.array.include'
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  | 'es2016.full'
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  | 'es2016.intl'
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  | 'es2017'
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  | 'es2017.arraybuffer'
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  | 'es2017.date'
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  | 'es2017.full'
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  | 'es2017.intl'
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  | 'es2017.object'
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  | 'es2017.sharedmemory'
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  | 'es2017.string'
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  | 'es2017.typedarrays'
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  | 'es2018'
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  | 'es2018.asyncgenerator'
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  | 'es2018.asynciterable'
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  | 'es2018.full'
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  | 'es2018.intl'
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  | 'es2018.promise'
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  | 'es2018.regexp'
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  | 'es2019'
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  | 'es2019.array'
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  | 'es2019.full'
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  | 'es2019.intl'
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  | 'es2019.object'
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  | 'es2019.string'
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  | 'es2019.symbol'
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  | 'es2020'
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  | 'es2020.bigint'
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  | 'es2020.date'
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  | 'es2020.full'
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  | 'es2020.intl'
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  | 'es2020.number'
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  | 'es2020.promise'
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  | 'es2020.sharedmemory'
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  | 'es2020.string'
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  | 'es2020.symbol.wellknown'
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  | 'es2021'
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  | 'es2021.full'
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  | 'es2021.intl'
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  | 'es2021.promise'
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  | 'es2021.string'
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  | 'es2021.weakref'
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  | 'es2022'
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  | 'es2022.array'
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  | 'es2022.error'
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  | 'es2022.full'
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  | 'es2022.intl'
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  | 'es2022.object'
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  | 'es2022.regexp'
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  | 'es2022.string'
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  | 'es2023'
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  | 'es2023.array'
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  | 'es2023.collection'
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  | 'es2023.full'
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  | 'es2023.intl'
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  | 'es2024'
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  | 'es2024.arraybuffer'
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  | 'es2024.collection'
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  | 'es2024.full'
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  | 'es2024.object'
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  | 'es2024.promise'
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  | 'es2024.regexp'
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  | 'es2024.sharedmemory'
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  | 'es2024.string'
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  | 'esnext'
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  | 'esnext.array'
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  | 'esnext.asynciterable'
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  | 'esnext.bigint'
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  | 'esnext.collection'
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  | 'esnext.decorators'
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  | 'esnext.disposable'
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  | 'esnext.error'
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  | 'esnext.float16'
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  | 'esnext.full'
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  | 'esnext.intl'
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  | 'esnext.iterator'
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  | 'esnext.object'
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  | 'esnext.promise'
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  | 'esnext.regexp'
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  | 'esnext.sharedmemory'
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  | 'esnext.string'
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  | 'esnext.symbol'
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  | 'esnext.weakref'
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  // Platform libraries
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  | 'dom'
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  | 'dom.asynciterable'
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  | 'dom.iterable'
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  | 'webworker'
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  | 'webworker.asynciterable'
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  | 'webworker.importscripts'
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  | 'webworker.iterable'
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  | 'scripthost'
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  // Feature libraries
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  | 'decorators'
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  | 'decorators.legacy'
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  | 'lib';
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```
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**Usage Examples:**
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```typescript
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import { Lib, ParserOptions } from "@typescript-eslint/types";
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// Basic modern web application
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const webAppLibs: Lib[] = [
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  'es2022',
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  'dom',
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  'dom.iterable'
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];
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// Node.js server application
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const nodeAppLibs: Lib[] = [
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  'es2021',
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  'es2021.promise'
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];
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// Configure parser with specific libraries
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const parserOptions: ParserOptions = {
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  lib: [
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    'es2023',           // Latest stable ECMAScript features
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    'dom',              // Browser DOM APIs
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    'dom.iterable',     // Iterable DOM collections
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    'webworker',        // Web Worker APIs
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    'decorators',       // Decorator support
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  ]
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};
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// Check if a library is ECMAScript-related
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function isECMAScriptLib(lib: Lib): boolean {
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  return lib.startsWith('es') || lib.startsWith('esnext');
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}
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// Get full feature set for a specific year
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function getFullLibForYear(year: number): Lib[] {
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  const baseLib = `es${year}` as Lib;
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  const fullLib = `es${year}.full` as Lib;
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  return [baseLib, fullLib];
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}
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```
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## Library Categories
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### ECMAScript Core Libraries
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Base ECMAScript version libraries:
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- **es5**: ECMAScript 5 (2009) - Basic JavaScript
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- **es6/es2015**: ECMAScript 2015 - Classes, modules, arrow functions
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- **es2016-es2024**: Annual ECMAScript releases with incremental features
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- **esnext**: Cutting-edge ECMAScript features (use with caution)
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### ECMAScript Feature Libraries
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Granular feature libraries for specific ECMAScript capabilities:
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- **Collection Libraries**: `es2015.collection`, `es2023.collection` - Map, Set, WeakMap, WeakSet
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- **Promise Libraries**: `es2015.promise`, `es2021.promise` - Promise APIs and enhancements
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- **Array Libraries**: `es2016.array.include`, `es2019.array`, `es2022.array` - Array methods
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- **String Libraries**: `es2017.string`, `es2019.string`, `es2022.string` - String methods
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- **Symbol Libraries**: `es2015.symbol`, `es2019.symbol` - Symbol functionality
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- **Async Libraries**: `es2018.asyncgenerator`, `es2018.asynciterable` - Async iteration
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### Platform Libraries
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Environment-specific APIs:
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- **DOM Libraries**: 
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  - `dom` - Browser DOM APIs (Document, Element, etc.)
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  - `dom.iterable` - Iterable DOM collections (NodeList, HTMLCollection)
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  - `dom.asynciterable` - Async iterable DOM APIs
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- **Web Worker Libraries**:
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  - `webworker` - Web Worker global scope
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  - `webworker.iterable` - Iterable APIs in workers
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  - `webworker.importscripts` - ImportScripts functionality
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- **Script Host**: `scripthost` - Windows Script Host APIs
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### Feature Libraries
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Specific language features:
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- **Decorators**:
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  - `decorators` - Stage 3 decorator proposal
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  - `decorators.legacy` - Legacy experimental decorators
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- **Special**: `lib` - Core library functionality
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### Full Libraries
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Comprehensive feature sets for specific versions:
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- **es2016.full**, **es2017.full**, etc. - Complete feature set for that ECMAScript version
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- **esnext.full** - All cutting-edge features
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**Common Library Combinations:**
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```typescript
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// Modern web application (React/Vue/Angular)
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const modernWebLibs: Lib[] = [
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  'es2022',
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  'dom',
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  'dom.iterable',
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  'es2022.array',
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  'es2022.string'
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];
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// Node.js backend service
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const nodeLibs: Lib[] = [
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  'es2021',
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  'es2021.promise',
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  'es2021.string',
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  'es2021.weakref'
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];
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// Browser extension
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const extensionLibs: Lib[] = [
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  'es2020',
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  'dom',
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  'webworker',
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  'scripthost'
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];
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// TypeScript with decorators
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const decoratorLibs: Lib[] = [
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  'es2023',
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  'decorators',
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  'dom'
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];
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// Legacy browser support
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const legacyLibs: Lib[] = [
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  'es5',
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  'dom'
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];
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// Cutting-edge features (experimental)
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const experimentalLibs: Lib[] = [
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  'esnext.full',
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  'esnext.decorators',
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  'esnext.disposable',
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  'dom'
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];
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```
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## Library Selection Guidelines
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### Version Selection Strategy
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1. **Start with base version**: Choose the oldest ECMAScript version your target environments support
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2. **Add specific features**: Include only the feature libraries you actually use
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3. **Include platform APIs**: Add `dom` for browsers, omit for Node.js
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4. **Consider future features**: Use `esnext` libraries carefully, prefer stable versions
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### Common Combinations
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- **Modern Web**: `['es2022', 'dom', 'dom.iterable']`
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- **Node.js Server**: `['es2021', 'es2021.promise']`
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- **Legacy Support**: `['es5', 'dom']`
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- **TypeScript with Decorators**: `['es2023', 'decorators', 'dom']`
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- **Web Worker**: `['es2020', 'webworker', 'webworker.iterable']`
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### Performance Considerations
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- Including more libraries increases TypeScript's memory usage
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- Only include libraries for APIs you actually use
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- Prefer specific feature libraries over `.full` libraries when possible
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- Test library combinations with your target environments