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TypeScript
Chapter 17
17 — Declaration Files & Ambient Types
Core Concepts
.d.tsfiles — type declarations without implementationdeclarekeyword — tells TS something exists without providing the code@typespackages — community-maintained type definitions (DefinitelyTyped)- Global declarations — make types available everywhere
- Module declarations — provide types for untyped packages
- Triple-slash directives — reference other declaration files
When You Need .d.ts Files
| Scenario | Solution |
|---|---|
| Untyped npm package | Install @types/package or write your own .d.ts |
| Global variables (window, env) | declare global { ... } |
| CSS modules, images | Module declaration: declare module "*.css" |
| Your own library | Generate with tsc --declaration |