安装

在开始前，请确保你有安装 Node.js 18 或更高版本。 然后，为你的应用创建一个目录并进入该目录。

mkdir myapp
cd myapp

使用 npm init 命令为你的应用创建一个 package.json 文件。 有关 package.json 工作机制的更多信息，请参阅 npm 的 package.json 处理细则。

npm init

yarn init

pnpm init

bun init

该命令会提示你输入一些信息，例如应用的名称和版本号。 目前，你可以直接按回车键接受大多数默认值，但以下情况除外：

entry point: (index.js)

输入 app.js，或者你希望作为主文件的其他名称。 如果希望使用 index.js，直接按回车键接受系统建议的默认文件名即可。

现在，在 myapp 目录中安装 Express，并将其保存到依赖列表中。 举个例子：

npm install express

yarn add express

pnpm add express

bun add express

如果只是临时安装 Express，而不将其加入依赖列表：

npm install express --no-save

bun add express --no-save

TypeScript

Express is written in JavaScript and does not bundle its own type definitions. To use it with TypeScript, install TypeScript together with the community-maintained types for Express and Node.js (from DefinitelyTyped) as development dependencies:

npm install --save-dev typescript @types/express @types/node

yarn add --dev typescript @types/express @types/node

pnpm add --save-dev typescript @types/express @types/node

bun add --dev typescript @types/express @types/node

Add a tsconfig.json. These options mirror how Node.js runs TypeScript and make the compiler reject non-erasable syntax (such as enums, namespaces, and parameter properties) that Node cannot strip:

{
  "compilerOptions": {
    "target": "esnext",
    "module": "nodenext",
    "rewriteRelativeImportExtensions": true,
    "erasableSyntaxOnly": true,
    "verbatimModuleSyntax": true,
    "noEmit": true,
    "strict": true,
    "skipLibCheck": true
  }
}

Write your application in TypeScript, annotating the request and response objects:

import express, { type Express, type Request, type Response } from 'express';

const app: Express = express();

app.get('/', (req: Request, res: Response) => {
  res.send('Hello World!');
});

app.listen(3000);

You do not need to annotate everything. When you pass a handler directly to a route method or to app.use(), Express infers the types of req, res, and next, and it infers route parameters from the path, so req.params.id is a string in app.get('/users/:id', ...). Add explicit types only where TypeScript has no context to infer from: error-handling middleware, whose (err, req, res, next) signature is not inferred, and handlers you define separately from the route. In those cases, annotate the parameters or type the whole function as RequestHandler or ErrorRequestHandler.

Run the file directly with Node.js, which strips the TypeScript types and runs the result without a build step:

node src/app.ts