Typescript文档7-JavaScript

https://www.typescriptlang.org/docs/handbook/intro-to-js-ts.html

2023.2.19 星期日

How to use TypeScript-powered JavaScript tooling.

JS Projects Utilizing TypeScript

The type system in TypeScript has different levels of strictness when working with a codebase:

A type-system based only on inference with JavaScript code

• Incremental typing in JavaScript via JSDoc
• Using // @ts-check in a JavaScript file
• TypeScript code
• TypeScript with strict enabled
  Each step represents a move towards a safer type-system, but not every project needs that level of verification.

  TypeScript with JavaScript

  Providing Type Hints in JS via JSDoc

  In a .js file, types can often be inferred. When types can’t be inferred, they can be specified using JSDoc syntax.

JSDoc annotations come before a declaration will be used to set the type of that declaration. For example:

/** @type {number} */
var x;
 
x = 0; // OK
x = false; // OK?!

@ts-check

To enable errors in your JavaScript files add: // @ts-check to the first line in your .js files to have TypeScript raise it as an error.

If you have a lot of JavaScript files you want to add errors to then you can switch to using a jsconfig.json. You can skip checking some files by adding a // @ts-nocheck comment to files.

TypeScript may offer you errors which you disagree with, in those cases you can ignore errors on specific lines by adding // @ts-ignore or// @ts-expect-erroron the preceding line.

// @ts-check
/** @type {number} */
var x;
 
x = 0; // OK
x = false; // Not OK
// Type 'boolean' is not assignable to type 'number'.

// @ts-expect-error
x = false; // Not OK

Type Checking JavaScript Files

JSDoc Reference

The list below outlines which constructs are currently supported when using JSDoc annotations to provide type information in JavaScript files.

Creating .d.ts Files from .js files