In this tutorial we’ll explore everything you’d learn in a standard 200 page book on TypeScript. I’ll cover installation, data types, changing the browser, arrays, math, looping, functions, classes, interfaces, inheritance, generic functions, generic classes, destructoring, template strings, spread operator, and many other topics.

All of the code follows the video below. My recommended TypeScript book is Pro TypeScript.

If you value videos like this consider contributing $1 on Patreon.

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Code & Cheat Sheet

// ---------- TypeScript ----------

// TypeScript brings a type system and future
// capabilities of JS today

// To compile TypeScript to JavaScript you
// must install a compiler
// Install Node at https://nodejs.org/en/

// Check that npm is installed OSX :
// sudo npm install npm -g

// Check that npm is installed Windows :
// npm install npm -g (As Admin)

// Type in your terminal : npm install -g typescript

// I'll use Ecmascript 5 in this tutorial

// Compile to JS with tsc tstut.ts --target ES5

// On Linux / OSX machines autocompile by typing
// tsc *.ts --watch --target ES5 in the terminal

// ---------- VARIABLES ----------

// Variables must start with a letter, _, or $
// and then can contain numbers

// Declaring variables as statically typed is optional
// If you only provide a value the type is inferred

var myName: string = "Derek";

var myAge: number = 41;

// booleans can only be true or false
var canVote: boolean = true;

// A variable marked as any is a dynamic type
var anything: any = "dog";
anything = 2;

// You can print in the defined element
document.getElementById("tsStuff").innerHTML = "My Name is " + myName;

// A variable that didn't get a value assigned
// gets undefined

// null is a user assigned value saying that
// no value is assigned

// typeof returns the data type
document.write("myName is a " + typeof(myName) + "<br />");
document.write("canVote is a " + typeof(canVote) + "<br />");
document.write("anything is a " + typeof(anything) + "<br />");

// We can convert strings to numbers
var strToNum: number = parseInt("5");
document.write("strToNum is a " + typeof(strToNum) + "<br />");

// toString() converts anything into a string
var numToStr: number = 5;
document.write("numToStr is a " + typeof(numToStr.toString()) + "<br />");

// You define constants with const
const PI = 3.14159;

// ---------- INTERFACES ----------
// An interface can be used to describe complex
// types

interface SuperHero {
  realName: String;
  superName: String;
}

var superman: SuperHero = {
  realName: "Clark Kent",
  superName: "Superman"
}

// It is best to always separate with +
document.write(superman.realName + " is " + superman.superName + "<br />");

// More on interfaces below

// ---------- ARRAYS ----------

// Creates an array of strings that only excepts
// string values
var employees: string[] = ["Bob", "Sally", "Sam"];

// This would cause an error
// employees.push(5);

// Print all values in array
document.write(employees.toString() + "<br />");

// You can create arrays of interfaces
var superheroes: SuperHero[] = [];

superheroes.push({
  realName: 'Bruce Wayne',
  superName: 'Batman'
});

document.write(superheroes[0].realName + " is " + superheroes[0].superName + "<br />");

// ---------- MATH ----------

document.write("5 + 4 = " + (5+4) + "<br />");
document.write("5 - 4 = " + (5-4) + "<br />");
document.write("5 * 4 = " + 5*4 + "<br />");
document.write("5 / 4 = " + 5/4 + "<br />");
document.write("5 % 4 = " + 5%4 + "<br />");

// If you try to add anything to a string both
// become strings
document.write("5 + String 2 = ", (5+'2') + "<br />");

var randNum: number = 1;

// If you increment after the current value is used
// and then it is incremented after
// The same is true with placing the -- after the
// variable
document.write("randNum++ = " + randNum++ + "<br />");
document.write("++randNum = " + ++randNum + "<br />");
document.write("randNum-- = " + randNum-- + "<br />");
document.write("--randNum = " + --randNum + "<br />");

// ---------- CONDITIONALS ----------
// If, Switch and the Ternary operator work
// the same in TypeScript as in JS

// Variables defined with let in blocks don't
// change the value of variables outside the block

let sampLet = 123;
if (true) {
    let sampLet = 456;
}
document.write("sampLet : " + sampLet + "<br />");

var sampVar = 123;
if (true) {
    var sampVar = 456;
}
document.write("sampVar : " + sampVar + "<br />");

// ---------- LOOPING ----------
// Looping works the same in TypeScript as in JS
// but for..of is added to get values in either
// an array or string

var randArray = [5,6,7,8];

// for..in provides the indexes
for(var val in randArray){
  document.write(val + "<br />");
}

// Convert a number array into a string array
var strArray = randArray.map(String)

// for..of provides the values
for(var val of strArray){
  document.write(val + "<br />");
}

// ---------- FUNCTIONS ----------

// You can assign the variable types for the attributes
// You assign the return type after the attributes
// or if nothing is returned use void
var getSum = function(num1: number, num2: number): number{
  return num1 + num2;
}

var theSum1: number = getSum(5,2);

document.write("5 + 2 = " + theSum1 + "<br />");

// Assign a default value in the function declaration
// If an attribute isn't required follow the variable
// with a ?
var getDiff = function(num1: number, num2 = 2, num3?: number): number{

  // Check if a value was assigned with typeof
  if (typeof num3 !== 'undefined'){
    return num1 - num2 - num3;
  }
  return num1 - num2;
}

document.write("5 - 2 = " + getDiff(5) + "<br />");
document.write("5 - 2 - 3 = " + getDiff(5,2,3) + "<br />");

// You can receive an unknown number of values
// with a rest parameter ...nums
var sumAll = function(...nums: number[]): void{

  // We can use reduce with the array to add all
  // the values together one by one
  var sum = nums.reduce((a, b) => a + b, 0);
  document.write("Sum : " + sum + "<br />");
}

sumAll(1,2,3,4,5);

// Arrow functions don't include function in
// the definition

var addOne = (x)=>x+1;

document.write("1 + 1 = " + addOne(1) + "<br />");

// ---------- CLASSES ----------

// Classes describe real world objects by defining
// their attributes (fields) and capabilities
// (methods)

class Animal {

  // class fields
  public favFood: string;

  // static fields have values that are shared
  // by every object
  static numOfAnimals: number = 0;

  // If you define an attribute with private
  // the value is automatically assigned
  constructor(private name: string, private owner: string){
    Animal.numOfAnimals++;
  }

  // You can define methods as private but then
  // it can't be seen by subclasses, or accessed
  // by any code other then that within the class
  ownerInfo() {
    document.write(this.name + " is owned by " + this.owner + "<br />");
  }

  // Static methods are accessed using the class
  // name
  static howManyAnimals(): number{
    return Animal.numOfAnimals;
  }

  // Define getters and setters

  private _weight: number;

  get weight(): number{
    return this._weight;
  }

  set weight(weight: number){
    this._weight = weight;
  }

}

// Create an Animal object
var spot = new Animal("Spot", "Doug");

spot.ownerInfo();

spot.weight = 100

document.write("Spot's weight is " + spot.weight + "<br />");

// You can only access static methods by proceeding
// it with the class name
document.write("# of Animals : " + Animal.howManyAnimals() + "<br />");

// You can inherit all methods and fields from
// another class with extends
// Additional methods and fields can be added
// or overwritten

class Dog extends Animal{
  constructor(name: string, owner: string){
    super(name, owner);
    Dog.numOfAnimals++;
  }
}

var grover = new Dog("Grover", "Jimmy");

// A call to howManyAnimals() is now 2
document.write("# of Animals : " + Animal.howManyAnimals() + "<br />");

// Use instanceof to check for inheritance
document.write("Is a Dog an Animal : " + (grover instanceof Animal) + "<br />");

// Check if a field exists for an object
document.write("Does grover have a name : " + ('name' in grover) + "<br />");

// ---------- INTERFACES 2 ----------
// Interfaces define a contract in which if a
// class implements it is must create all
// functions defined in the interface

interface Vehicle {
  drive(): any;
}

class Car implements Vehicle{
  constructor(private wheels: number){}

  drive(): void{
    document.write("The car drives with " + this.wheels + " wheels<br />");
  }
}

class Bicycle implements Vehicle{
  constructor(private wheels: number){}

  drive(): void{
    document.write("The bicycle drives with " + this.wheels + " wheels<br />");
  }
}

var car = new Car(4);
var bike = new Bicycle(2);

car.drive();
bike.drive();

// ---------- GENERIC FUNCTIONS ----------
// We use generic functions when we want
// to be able to work with multiple data
// types in similar ways

// To create a generic function we place
// 1 or more data type markers in angled
// brackets after the function name. We
// then use those data type markers
// instead of actual data types.

function GetType<T>(val: T): string{
  return typeof(val);
}

var aStr = "A String";
var aNum = 10;

document.write(GetType(aStr) + "<br />");
document.write(GetType(aNum) + "<br />");

// You define a generic function that
// excepts any class that implements
// an interface

function GetWheels<w extends Vehicle>(veh: w): number
{
  return veh.drive();
}

GetWheels(car);
GetWheels(bike);

// You can also define generic classes that
// can work with multiple data types

class GenericNumber<T>{

  // An arrow function as described above
  add: (val1: T, val2: T) => T;
}

var aNumber = new GenericNumber<number>();

// Define how we want add to work with numbers
aNumber.add = function(x, y){return x + y;};

document.write("5 + 4 = " + aNumber.add(5, 4) + "<br />");

var aStrNum = new GenericNumber<string>();

// Define how we want add to work with strings
aStrNum.add = function(x, y){return String(Number(x) + Number(y));};

document.write("5 + 6 = " + aStrNum.add("5", "6") + "<br />");

// ---------- DESTRUCTORING ----------
// You can assign multiple values on one line

var randVals = {x: 1, y: 2, z: 3};
var {x, y, z} = randVals;

document.write(x + y + z + "<br />");

// Do the same with arrays
[x, y, z] = [z, y, x];
document.write("Switch : " + x + y + z + "<br />");

// ---------- TEMPLATE STRINGS ----------
// Create multiline strings
var multStr = `I go on for
many lines<br />`;
document.write(multStr);

// You can use string interpolation
document.write(`<b>${multStr}</b>`);

// ---------- SPREAD OPERATOR ----------
// We can separate values in an array into
// attributs in a function

function theSum(x, y, z): void{
  document.write("Sum : " + (x + y + z) + "<br />");
}

var args = [4, 5, 6];

theSum(...args);

// ---------- ENUMS ----------
// Enums are number based in TS

enum Emotion {
  Happy = 1,
  Sad,
  Angry
};

var myFeeling = Emotion.Happy;

// Same as

myFeeling = 1;