node.js - typescript + Express : Type 'typeof e' has no compatible call signatures

Question

我正在尝试使用 typescript express来构建应用程序。但我收到此错误:Cannot invoke an expression whose type lacks a call signature. Type 'typeof e' has no compatible call signatures(在名为express()的app.ts中)

我在这里使用webpack来帮助我的开发。

我的Package.json:

"scripts" :{
    "build": "webpack" 
 },
 "dependencies": {
    "body-parser": "^1.18.3",
    "dotenv": "^6.1.0",
    "jsonwebtoken": "^8.3.0",
    "nodemon": "^1.18.5"
  },
  "devDependencies": {
    "@types/body-parser": "^1.17.0",
    "@types/dotenv": "^4.0.3",
    "@types/express": "^4.16.0",
    "clean-webpack-plugin": "^0.1.19",
    "ts-loader": "^5.3.0",
    "ts-node": "^7.0.1",
    "typescript": "^3.1.6",
    "webpack": "^4.24.0",
    "webpack-cli": "^3.1.2"
  }

我的 webpack.confg.js:

var path = require("path");
const CleanWebpackPlugin = require("clean-webpack-plugin");

var fs = require("fs");
var nodeModules = {};
fs.readdirSync("node_modules")
  .filter(function(x) {
    return [".bin"].indexOf(x) === -1;
  })
  .forEach(function(mod) {
    nodeModules[mod] = "commonjs " + mod;
  });

module.exports = {
  entry: "./src/index.ts",

  plugins: [new CleanWebpackPlugin(["./dist"])],
  output: {
    filename: "index.js",
    path: path.resolve(__dirname, "dist")
  },
  module: {
    rules: [
      //all files with .ts extention will be handled y ts-loader
      { test: /\.ts$/, loader: "ts-loader" }
    ]
  },
  target: "node",
  externals: nodeModules
};

我的 app.ts:

import * as express from "express";
import * as bodyParser from "body-parser";

class App {
  public app: express.Application;
  constructor() {
    this.app = express();
    this.config();
  }

  private config(): void {
    //add support for application/json type for data
    this.app.use(bodyParser.json());

    //support application/x-www-form-urlencoded post data
    this.app.use(bodyParser.urlencoded({ extended: false }));
  }
}

export default new App().app;

我正在运行 npm run build，并且构建失败并显示错误。
尝试在一些博客中寻找解决方案，但都没有提到有关此错误的tanything。我设法将 express.Application作为 app的类型添加到一侧 app.ts中
我究竟做错了什么 ？是否由于webpack的配置？

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Answer 1

您需要从express而不是 namespace (这是具有所有已命名导出的对象)中导入默认导出。

在您的app.ts中，这应该是您所需要的:

// Change these
import express from "express";
import bodyParser from "body-parser";

区别在于:

// Namespace import
import * as express from "express";

const app = express.default();

// Default import
import express from "express";

const app = express();