typescript - 如何使用 import 而不是 require 创建 express 应用程序

Question

这就是 require 的作用。我们希望它使用 import。

import { Request, Response, Application } from 'express';

// TODO Figure out how NOT to use require here.
const express = require('express');
var app: Application = express();

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

app.listen(3000);

我们尝试过的

我们的 tsconfig.json 有 "esModuleInterop": true。

尝试#1

import express from 'express';

这给出了这个错误:

"node_modules/@types/express/index"' has no default export.ts

尝试#2

import * as express from 'express';
var app = express();

这给出了不同的错误:

Cannot invoke an expression whose type lacks a call signature. Type 'typeof e' has no compatible call signatures.ts(2349) index.ts(1, 1): Type originates at this import. A namespace-style import cannot be called or constructed, and will cause a failure at runtime. Consider using a default import or import require here instead.

Answer 1

TypeScript 有 special import syntax处理将函数或其他一些自定义对象作为一个整体导出的模块(不是默认导出):

import { Request, Response, Application } from 'express';
import express = require('express');

var app: Application = express();

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

app.listen(3000);

---

或者，您可以使用 TypeScript 编译器选项来更改导入的模块，以便它们具有默认导出:

// tsconfig.json
{
  "compilerOptions": {
    "allowSyntheticDefaultImports": true,     /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
    "esModuleInterop": true,                  /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
  }
}

并使用此默认导入进行导入:

import express from 'express' 
var app = express();