Typescript + Express : Type 'typeof e' has no compatible call signatures

Question

I'm trying to build an application using typescript , express . but i'm getting this error : Cannot invoke an expression whose type lacks a call signature. Type 'typeof e' has no compatible call signatures(in app.ts where express() is called )

I'm using webpack here to help with my development.

My 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"
  }

my 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
};

my 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;

I'm running npm run build and my build fails with the error stated . tried searching for solution in a few blogs and none have mentioned tanything about this error .I manged to add express.Application as type for app in side app.ts What am i doing wrong ? Is it because of the configuration of webpack ?

Any help appreciated

Answer 1

You need to import the default export from express instead of the namespace (which is an object with all named exports).

In your app.ts this should be all you need:

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

The difference is:

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

const app = express.default();

// Default import
import express from "express";

const app = express();