TypeScript

TypeScript is a language that builds on JavaScript by adding syntax for type declarations and annotations. It is a superset of JavaScript and is maintained by Microsoft.

Documentation

Usage

npx ayanokoji typescript init

This command initializes TypeScript in your project through an interactive process where you can configure:

• Strictness settings (strict mode, noUncheckedIndexedAccess, noImplicitOverride)
• Transpilation method (tsc vs other build tools)
• Runtime environment (browser DOM vs Node.js)
• Library configuration
• Monorepo settings
• Dependencies to install (TypeScript, @types/node, @types/bun, @cloudflare/workers-types)

The command creates a tsconfig.json with optimized defaults including:

• ES2022 target
• Module resolution for Node.js/ESM
• JSON module support
• Source map generation
• Strict type checking (optional)

The command will fail if a tsconfig.json file already exists in your project.

TSConfig Options

The generated tsconfig.json includes carefully selected options:

Base Options

• target: "es2022" - Compiles to modern JavaScript features
• esModuleInterop: true - Enables cleaner imports from CommonJS modules
• skipLibCheck: true - Skips type-checking of declaration files for better performance
• allowJs: true - Allows JavaScript files to be imported
• resolveJsonModule: true - Enables importing JSON files
• moduleDetection: "force" - Treats each file as a module
• verbatimModuleSyntax: true - Ensures explicit imports/exports
• erasableSyntaxOnly: true - Limits TypeScript syntax to features that can be easily erased to JavaScript. Disallows enums, namespaces with runtime code, parameter properties in classes, and non-ECMAScript import/export assignments.

  // ❌ error: An `import ... = require(...)` alias
  import foo = require("foo");
  // ❌ error: A namespace with runtime code.
  namespace container {
    foo.method();
    export type Bar = string;
  }
  // ❌ error: An `import =` alias
  import Bar = container.Bar;
  class Point {
    // ❌ error: Parameter properties
    constructor(public x: number, public y: number) {}
  }
  // ❌ error: An `export =` assignment.
  export = Point;
  // ❌ error: An enum declaration.
  enum Direction {
    Up,
    Down,
    Left,
    Right,
  }

Strictness Options (Optional)

• strict: true - Enables all strict type checking options.
• noUncheckedIndexedAccess: true - Adds undefined to indexed access like array[0].
• noImplicitOverride: true - Ensures explicit override keywords for inherited methods.

Build Options

When using tsc:

• moduleResolution: "NodeNext" - Modern Node.js module resolution.
• module: "NodeNext" - Uses Node.js module format.
• outDir: "dist" - Outputs compiled files to dist folder.
• sourceMap: true - Generates source maps for debugging.

When using other build tools:

• moduleResolution: "Bundler" - Modern bundler-style resolution.
• module: "Preserve" - Preserves the original module syntax.
• noEmit: true - Skips generating output files.

Library Options (Optional)

• composite: true - Tells TypeScript to emit .tsbuildinfo files. This tells TypeScript that your project is part of a monorepo, and also helps it to cache builds to run faster.
• declaration: true - Tells TypeScript to emit .d.ts files. This is needed so that libraries can get autocomplete on the .js files you're creating.
• declarationMap: true - Generates source maps for .d.ts files. These are needed so that when consumers of your libraries are debugging, they can jump to the original source code using go-to-definition.