TypeScript is JavaScript with syntax for types.

TypeScript is a strongly typed programming language that builds on JavaScript, giving you better tooling at any scale.

ts
const user = {
firstName: "Angela",
lastName: "Davis",
role: "Professor",
}
 
console.log(user.name)
Property 'name' does not exist on type '{ firstName: string; lastName: string; role: string; }'.2339Property 'name' does not exist on type '{ firstName: string; lastName: string; role: string; }'.
 
ts
const user = {
firstName: "Angela",
lastName: "Davis",
role: "Professor",
}
 
console.log(user.name)
Property 'name' does not exist on type '{ firstName: string; lastName: string; role: string; }'.2339Property 'name' does not exist on type '{ firstName: string; lastName: string; role: string; }'.
 

TypeScript 4.4 已经发布, 4.5 目前在 beta 测试中。

What is TypeScript?

JavaScript and More

TypeScript adds additional syntax to JavaScript to support a tighter integration with your editor. Catch errors early in your editor.

A Result You Can Trust

TypeScript code converts to JavaScript, which runs anywhere JavaScript runs: In a browser, on Node.js or Deno and in your apps.

Safety at Scale

TypeScript understands JavaScript and uses type inference to give you great tooling without additional code.

Adopt TypeScript Gradually

Apply types to your JavaScript project incrementally, each step improves editor support and improves your codebase.

Let's take this incorrect JavaScript code, and see how TypeScript can catch mistakes in your editor.

js
function compact(arr) {
if (orr.length > 10)
return arr.trim(0, 10)
return arr
}

No editor warnings in JavaScript files

This code crashes at runtime!

JavaScript file

js
// @ts-check
 
function compact(arr) {
if (orr.length > 10)
Cannot find name 'orr'.2304Cannot find name 'orr'.
return arr.trim(0, 10)
return arr
}

Adding this to a JS file shows errors in your editor

the param is arr, not orr!

JavaScript with TS Check

js
// @ts-check
 
/** @param {any[]} arr */
function compact(arr) {
if (arr.length > 10)
return arr.trim(0, 10)
Property 'trim' does not exist on type 'any[]'.2339Property 'trim' does not exist on type 'any[]'.
return arr
}

Using JSDoc to give type information

Now TS has found a bad call. Arrays have slice, not trim.

JavaScript with JSDoc

ts
function compact(arr: string[]) {
if (arr.length > 10)
return arr.slice(0, 10)
return arr
}

TypeScript adds natural syntax for providing types

TypeScript file

Describe Your Data

Describe the shape of objects and functions in your code.

Making it possible to see documentation and issues in your editor.

ts
interface Account {
id: number
displayName: string
version: 1
}
 
function welcome(user: Account) {
console.log(user.id)
}
ts
type Result = "pass" | "fail"
 
function verify(result: Result) {
if (result === "pass") {
console.log("Passed")
} else {
console.log("Failed")
}
}

TypeScript becomes JavaScript via the delete key.

ts
type Result = "pass" | "fail"
 
function verify(result: Result) {
if (result === "pass") {
console.log("Passed")
} else {
console.log("Failed")
}
}
 

TypeScript file.

ts
type Result = "pass" | "fail"
 
function verify(result: Result) {
if (result === "pass") {
console.log("Passed")
} else {
console.log("Failed")
}
}
 

Types are removed.

js
 
 
function verify(result) {
if (result === "pass") {
console.log("Passed")
} else {
console.log("Failed")
}
}
 

JavaScript file.

TypeScript Testimonials

First, we were surprised by the number of small bugs we found when converting our code.

Second, we underestimated how powerful the editor integration is.

TypeScript was such a boon to our stability and sanity that we started using it for all new code within days of starting the conversion.

Felix Rieseberg at Slack covered the transition of their desktop app from JavaScript to TypeScript in their blog

Read

Loved by Developers

Image of the stack overflow logo, and a graph showing TypeScript as the 2nd most popular language

Voted 2nd most loved programming language in the Stack Overflow 2020 Developer survey

Logo of the State of JS survey

TypeScript was used by 78% of the 2020 State of JS respondents, with 93% saying they would use it again.

TypeScript was given the award for “Most Adopted Technology” based on year-on-year growth.