At this step we will continue refactoring our application, we will use TypeScript modules to organise our project and make it maintainable.

One important note about terminology from official TypeScript documentation: > It’s important to note that in TypeScript 1.5, the nomenclature has changed. “Internal modules” are now “namespaces”. “External modules” are now simply “modules”, as to align with ECMAScript 2015’s terminology, (namely that module X { is equivalent to the now-preferred namespace X {).

Also please consider note from TypeScript Deep Dive: > For most projects we recommend using external modules and using namespace for quick demos and porting old JavaScript code.

So we won’t use namespace for this WorkShop and go to modules.

I. Creating folders, installing jQuery and modifying tsconfig.json

We start with creating two folders: - src - will contain source files in TypeScript; - dist - compiled JavaScript files will go here.

Also instead of CDN we will install jQuery as npm package. This console command will install jQuery 2.x into node_modules folder:

npm install --save jquery@2

Next, we will make modifications in tsconfig.json file. We will remove files section and replace it with include, also we add two options to include jQuery into project - baseUrl and paths at last we will add option outDir and specify where to output compiled files.

Our tsconfig.json will look like this:

    "compilerOptions": {
        "sourceMap": true,
        "watch": true,
        "noEmitOnError": true,
        "experimentalDecorators": true,
        "target": "es5",
        "baseUrl": ".", // This must be specified if "paths" is.
        "paths": {
            "jquery": ["node_modules/jquery/dist/jquery"]
        "outDir": "./dist/"
    "include": [

II. Split index.ts into multiple files

Then we will split our index.ts into several files and put them into src folder.

First, extract function DOMElement and place it into file dom-element.ts:


export default function DOMElement(value: string): any {
    return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) {
        const oldMethod = target[propertyKey];
        descriptor.value = function(...args: any[]){
            return `<${value}>${oldMethod.apply(this, args)}</${value}>`;
        return descriptor;

As you can see, we added export default before function name to tell compiler that we export it as default component of the module.

Next, we will extract classes Task and HighPriorityTask into file tasks.ts:


import DOMElement from './dom-element';

export default class Task {
    private priority: number;
    private title: string;
    constructor(priority: number, title: string) {
        this.priority = priority;
        this.title = title;

    toString(): string {
        return `Priority: ${this.priority}, Title: ${this.title}`;

export class HighPriorityTask extends Task {
    toString(): string {
        return super.toString();

Please note that we we added import statement at the top of the file to tell that we are importing DOMElement.

Also we will place our TaskFactory into file task-factory.ts and also use import to tell that we rely on Task and HighPriorityTask:


import {default as Task, HighPriorityTask} from './tasks';

export default class TaskFactory {
    static getTask(priority: number, title: string): Task {
        if (priority === 1) {
            return new HighPriorityTask(priority, title);
        } else {
            return new Task(priority, title);

At last we will move our index.ts file into src folder and place imports on top of it, please note that we changed how we are adding jQuery to the project - instead of <script> tag in index.html we use import statement:


import * as $ from 'jquery';
import Task from './tasks';
import TaskFactory from './task-factory';

let tasks: Task[] = [];
$('#btn-add').click(function (e) {
    const task = TaskFactory.getTask(Number($('#task-priority').val()), $('#task-title').val());
    let domString = '';
    tasks.forEach(t => domString += t);

III. Add SystemJS module loader

After making all modifications to our file structure we restart TypeScript compiler and will receive compiled JavaScript files in dist folder. To use them on our html page we could add multiple <script> tags but there is another option to do it right way - use module loader.

We will use SystemJS module loader.

To install it we will execute following command:

npm i systemjs

Then in our index.html file instead of single <script> tag referencing index.js we will add reference to SystemJS and configure it to run our project:

Our index.html will look like:

<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Ultimate ToDo</title>
    <h1>Ultimate ToDo List</h1>
    <ul id="task-list"></ul>
    <h3>New task:</h3>
        <label for="task-priority">Priority:</label>
        <input type="text" id="task-priority">
        <label for="task-title">Title:</label>
        <input type="text" id="task-title">
        <button id="btn-add">Add</button>
    <script src="node_modules\systemjs\dist\system.js"></script>
            baseURL: '.',
            map: {
                jquery: 'node_modules/jquery/dist/jquery.js'
            packages: {
                'dist': {
                    main: 'index.js',
                    defaultExtension: 'js', 
                    defaultJSExtensions: true

See source code for this step on GitHub