Typescript 2 — using ES6 import & require?

Question

I have an exported class in my working Angular2 app using ES6 module:

//File = init.todos.ts

export class Init {
   load() {
      ...
    }
}

I'm importing this class from another component via :

//File = todo.service.ts

import { Init } from './init.todos'

It works as expected.

However if I change the loading mechanism to commonjs :

//File = init.todos.ts
export class Init {
    load() {
       ...
    }
}
 module.exports.Init = Init;

Requiring it:

//File = todo.service.ts
var  Init = require("./init.todos");

— I get those errors :

...myApp/src/app/todo.service.ts (4,13): Cannot find name 'require'.) ...myApp/src/app/todo.service.ts (12,14): Property 'load' does not exist on type 'TodoService'.)

Question:

How can I also load commonjs modules using require ?

Tsconfig.json:

{
    "compileOnSave": false,
    "compilerOptions": {
        "outDir": "./dist/out-tsc",
        "baseUrl": "src",
        "module": "system",
        "sourceMap": true,
        "declaration": false,
        "moduleResolution": "node",
        "emitDecoratorMetadata": true,
        "experimentalDecorators": true,
        "target": "es5",
        "typeRoots": [
            "node_modules/@types"
        ],
        "lib": [
            "es2016",
            "dom"
        ]
    }
}

Here are the config files :

tslint.json

tsconfig.json

package.json

angular-cli.json

webpack.config.js

Answer 1

Since version 1.5 , Typescript has adopted the ES6 style of imports.

You can keep your code "as is"

//File = init.todos.ts

export class Init {
   load() {
      ...
    }
}

//File = todo.service.ts

import { Init } from './init.todos'

By moving the property module in tsconfig.json to commonjs , the transpiler will generate commonjs compatible javascript which will allow you to benefit from, and contribute to, the full nodeJS ecosystem.

"compileOptions": {
    ...
    "module": "commonjs"
    ...
}

If you wish to import an existing NodeJS module in your typescript code, a few things may happen

• the module ships with embedded Typescript Definition Files (there is a "typings" entry in "package.json"). In that case, import the module using the ES6 syntax and you are good to go ( import * as blah from 'blah' ). immutable.js is a good example of such a library

• the module does not ship with Definition files but there is one available on DefinitelyTyped , simply

  • run npm install @types/blah to get the definitions in your project
  • and import the module as usual: import * as blah from 'blah'

• the module does not have a definition file

  • you can craft one, simply add it to your project after naming it blah.d.ts . DefinitelyTyped has a guide on this
  • you can decide to go without typings, simply use NodeJS require() const blah = require('blah') , and blah will have type any (which really means that blah opted out of typing)

(for sake of completeness, I could add the allowJS compiler option available since 1.8, but that is a whole subject in itself)

Answer 2

TypeScript is ES6 compliant. Use ES6 module loading syntax within your TypeScript source files:

import  { SomeType } from './some.module';

When TypeScript compiles to regular JavaScript, you can target a module system of your choosing:

"compileOptions": {
    "module": "commonjs" (or system, umd, amd)
}

Whatever target module system you choose, you need to ensure that you include the necessary scripts and configuration to load the module. ie SystemJS, RequireJS, etc.

As an exercise, try targeting different module loaders, and inspect the .js file - you'll see what I mean.

Answer 3

the problem of your question actually is not the require(...) method.it is that you reference error Init.I think you want to lazy load modules via require.but you load class that contains an instance method load (it is not a class method,if you want you must declaring it as static ).so you must create an instance before you use it.by default,require(...) return any

declare function require(id: string): any;

if you want typescript infer type correctly you must declare require() return type,eg: let foo:typeof Foo = require('foo') .I found that the ts-jest test pass when module is anything except system because it is lazy loading,not execute test definition immediately,so I'm sure the problem is not the module. here is my test code:

Test

//for inferer type for typescript
//This leverages the reference-elision optimization,
//so that the module is only loaded when needed.
//so use InitClass as a type will skipped.
import {Init as InitClass} from  "./init.todos";

test("typescript dynamic load supports inferer types", () => {
    let Init: typeof InitClass = require("./init.todos").Init;

    let it = new Init();
    expect(it.load()).toEqual("bar");
});