Demystifying TypeScript

5 Common Myths Debunked

by Kamran Ayub / @kamranayub


Yes, that's me with a monkey...


Writing large JavaScript applications is hard

The Mystical TypeScript


Myth #1

“TypeScript is not interoperable with JavaScript”


“I have to rewrite my JavaScript codebase”

What language is this?

var Point = function (x, y) { 
	this.x = x; 
	this.y = y; 
Point.prototype.distance = function (other) {
	other = other || new Point(0.0, 0.0);
	return Math.sqrt(
		Math.pow(this.x - other.x, 2) + 
		Math.pow(this.y - other.y, 2));

var p1 = new Point(5, 6);
var p2 = new Point(1, 1);

// Calculate distance between two points
console.log("Distance between", p1, p2, "is", p1.distance(p2));

It's JavaScript!

And it's TypeScript!

All valid JavaScript is valid TypeScript


  • TypeScript compiles into plain old JavaScript
  • Static typing is totally optional, but encouraged
  • There is no overhead because TypeScript does not run in the browser

Quick Example: Get Started

Declaration Files

Declaration files make it easy to work with existing libraries

Quick Example: Moment.js

Myth #1

“TypeScript is not interoperable with JavaScript”


TypeScript is a typed superset of JavaScript that compiles down to plain, human-readable JavaScript

Myth #2

“I have to learn a whole new language”


“I have to re-learn JavaScript, my existing skills are useless”

Yes and No

Are there new language features to learn? Yes

Is it a whole new language? No


  • TypeScript brings ES2015 & ES2016 to you now
  • You will probably learn the new syntax anyway
  • There are only a few a handful of new things to learn
  • TypeScript can target different versions of ECMAScript
  • TypeScript is forward-compatible

TypeScript & ES2015 Share:

Classes, arrow functions, let/const, default parameters, rest parameters, string interpolation, for..of, symbols

TypeScript layers on:

Interfaces, enums, namespaces, optional parameters, overload functions, abstract classes, class member accessibility/visibility, static typing, generics, union types, type guards, intersection types, type aliasing


Example: classes.ts


Example: generics.ts

Type Unions and Guards

Example: unions.ts

Learn more:

TypeScript Handbook

TypeScript Release Notes

Myth #2

“I have to learn a whole new language”


Existing experience transfers directly. Much of the syntax and features are designed to be forward-compatible with ES2015 and ES2016 while maintaining maximum backwards-compatibility.

Myth #3

“You can only use TypeScript in Windows”


“My platform isn't supported!”


  • The TypeScript compiler and language service is open-source
  • You can use TypeScript on any platform and any OS
  • You can integrate TypeScript into any editor of your choice

Windows First-Class Experience

Visual Studio Community 2015

Community edition is free and fully supports extensions

Cross-Platform First-Class Experience

Visual Studio Code

Cross-platform on Linux, Mac, and Windows. Full TypeScript (w/Chrome & Node.js debugging) support plus tons more.

Monthly release cycle

And there's more...

Download for your platform and editor of choice

VS Code Example

Myth #3

“You can only use TypeScript in Windows”


TypeScript is open-source, has awesome cross-platform tooling, and can integrate with just about any editor you use

Myth #4

“Unit testing will eliminate any need of TypeScript”


“I don't need no stinkin' type checking”

Consider the following

“Alright, just saved my script, let's run it!”
TypeError: undefined is not a function
(╯°□°)╯︵ ┻━┻


Sound Familiar?

How about this?

“We should refactor one of the parts of this app!”

A Read-Only Codebase Is Not Good

The sad truth

Not everyone writes JavaScript unit tests

(including yours truly)

Even if you have tests


  • eliminates an entire class of errors
  • allows richer developer tooling (Intellisense!)
  • makes your codebase leaner and easier to refactor
  • is opt-in—use as much or as little as you want
  • is pretty easy to learn

If you are used to strongly-typed languages,
you'll feel right at home

A practical example

Myth #4

“Unit testing will eliminate any need of TypeScript”


TypeScript is refactor-friendly, can catch easily overlooked errors, reduces risk of runtime errors, and allows you to reason about your codebase better

You should still totally write tests, though

Myth #5

“TypeScript is like CoffeeScript or Dart or Babel, or Flow, etc.”


“Don't we already have this?”



class Point
  constructor(@x, @y) ->

  distance(other) ->
    dx = @x - other.x
    dy = @y - other.y
    Math.sqrt dx * dx + dy * dy
  • Is a separate language that compiles into JavaScript
  • Inspired by Ruby & Python (ft. significant whitespace)
  • Does not feature static typing
  • Is more of a "macro" or expansion w/syntactic-sugar language


import 'dart:math';

class Point {
  num x;
  num y;

  Point(this.x, this.y);

  num distance(Point p) {
    num dx = x - p.x;
    num dy = y - p.y;
    return sqrt(dx * dx + dy * dy);
  • Full on SDK/framework and language
  • Supports static types
  • Compiles into non-idiomatic JavaScript
  • Can run in a Dartium VM (extra perf)


  • Is not a language or framework, it's a compiler
  • Compiles ES2015 to ES5 backwards-compatibility
  • Supports extensible polyfill system
  • Is not necessarily mutually exclusive from TS

You should definitely consider using it if you aren't going to use TypeScript


/* @flow */

class Point {
	x: number;
	y: number;

	constructor(x: number, y: number) {
		this.x = x;
		this.y = y;

	distance(p: Point) {
		var dx = this.x - p.x;
		var dy = this.y - p.y;

		return Math.sqrt(dx * dx + dy * dy);
  • Is eerily similar to TypeScript (checker vs. compiler)
  • Has nullable types (TS 2.0?)
  • Doesn't have visibility/accessibility modifiers
  • Can use babel.js to transpile to vanilla JS vs. integrated tooling

This is the closest to TypeScript you can get


class Point {
  constructor(public x: number, public y: number) {


  distance(p: Point) {
    var dx = this.x - p.x;
    var dy = this.y - p.y;

    return Math.sqrt(dx * dx + dy * dy);
  • Good middle-ground, outputs idiomatic JavaScript
  • Adds static typing, friendly to Java/C-based language devs
  • Forwards-compatible syntax with ES2015, ES2016, etc.
  • Rich editor tooling & intellisense
  • Simpler, "It's just JavaScript!™"

Myth #5

“TypeScript is like CoffeeScript or Dart or Babel.js or Flow”


There are huge fundamental differences between these languages/frameworks/tools (but Flow is really damn close)

Practical Use Cases


I've used TypeScript for over three years now in my own game(s) and apps

Assists in maintaining good structure and organization of our code


Excalibur.js (the engine I work on) is written in TypeScript

Angular 2 is written in TypeScript

Provides type-safe API and type-rich documentation

Provides structure and organization to your framework

Great for OSS projects where others can contribute

Large Applications

Visual Studio Code is written in TypeScript

The Microsoft Azure Blade UI (portal) is written in TypeScript

Angular 2 apps are using TypeScript

Great fit for "enterprisey" apps and projects with rotating team members

Do you truly enjoy the loosey-goosey nature of Javascript all the time?

It wasn't designed for scale. TypeScript is.

Go and get things done.

Thank you

@kamranayub /



For your perusal

Watch my TypeScript in Action Talk

Read some thoughts on whether static type checking actually helps

Go through Flow vs. TypeScript by Oliver Zeigermann

Credits: Title border designed by Freepik