Reputation: 920

import module typescript error

When I import a module in a app.ts script, the '.js' file extension is missing in the import line of the compiled js file.

app.ts import {ModuleA} from './ModuleA'

compiled app.js import {ModuleA} from './ModuleA';

I include it in the html file like this <script type="module" src="app.js"></script>

But the browser can't find the module 'ModuleA'.

It only work when I import like this import {ModuleA} from './ModuleA.js'

But I want to work by importing '.ts' module files, not '.js' module files.

I would have hoped the ts compilation add the '.js' extension to the import line.

Any suggestions?

Upvotes: 0

Answers (3)

Kent Weigel

Reputation: 1178

When you don't specify compiler options on the command line for tsc and you don't have a tsconfig.json file, typescript uses defaults. According to the typescript documentation the defaults are es3 for the language emitted, and commonjs for the module loader. I don't find these options acceptable, so I specify different options in a tsconfig.json file. Try setting up a project as follows and I think you'll be happy with the results. It may seem like a lot of work, but you can export the project to a template when your done, and you won't ever have to do it again. This assumes you have npm set up on your machine.

Create a new project in VS 2017, choosing ASP.NET Web Application(.NET Framework) as the template. I know this may not sound right, but bear with me, as you will end up with a minimal project that doesn't include much that you don't want. On the next page of the wizard, choose Empty and un-check every box and leave it with no authentication. Finish the wizard.

Add the following files at the root level of the project.

package.json:

{
  "version": "1.0.0",
  "name": "asp.net",
  "author": "you",
  "private": true,
  "dependencies": {
    "core-js": "^2.5.3",
    "systemjs": "^0.21.0"
  }
}

tsconfig.json:

{
  "compilerOptions": {
    "module": "system",
    "target": "es5",
    "noImplicitAny": true,
    "noEmitOnError": true,
    "sourceMap": true
  },
  "files": [
    "app/app.ts"
  ],
  "exclude": [
    "node_modules"
  ]
}

system.config.js:

(function (global) {
  SystemJS.config({
    paths: {
      'npm:': '/node_modules/'
    },
    map: {
      app: '/app'
    },
    packages: {
      app: {
        main: 'app.js',
        defaultExtension: 'js'
      }
    }
  })
})(this);

index.html:

<!DOCTYPE html>
<html>
<head>
  <base href="/" />
  <meta charset="utf-8" />
  <title>Typescript with SystemJS and Modules Demo</title>
  <script src="node_modules/core-js/client/shim.min.js"></script>
  <script src="node_modules/systemjs/dist/system.js"></script>
  <script src="system.config.js"></script>
  <script>
    SystemJS.import("app/app.js").catch(function (e) { console.log(e); });
  </script>
</head>
<body>
  <div id="personDiv"></div>
</body>
</html>

Also, create an app folder and put the following 2 files in it:

app.ts:

import { Person } from "./person";

export class App {
  constructor() {
    let person: Person = new Person();
    let div: HTMLDivElement = <HTMLDivElement>document.getElementById('personDiv');
    div.innerHTML = person.getName();
  }
}

// Use this assignment to start execution.
let a: App = new App();

// The following doesn't appear to work with SystemJS. It does with plain TypeScript.
// It is probably because SystemJS already defines a listener for window.onload,
// although I haven't verified that.
//window.onload = () => {
//  let a: App = new App();
//  let person = new Person();
//  alert(person.getName);
//}

person.ts:

export class Person {
  fullName: string;

  constructor() {
    this.fullName = "Test Guy";
  }

  getName():string {
    return this.fullName;
  }
}

Then build and run the app. The results should show you that importing is working correctly.

Upvotes: 1