You can install and start watching typescript compilation using

npm install -g typescript
tsc -w

Types are checked when you assign or use method on it.

Basic types

  • boolean, number, string for example let name: string = 'Duke';
  • _[] or Array<_>: let list: number[] = [1, 2, 3];, generic array type: let list: Array<number> = [1, 2, 3];
    • type is used when array has different types let x: [string, number] so first element is string and second is number, and all others are union of those (string | number).
  • enum Color {Red, Green. Blue} usage is let c: Color = Color.Red. By default value is 0, 1, … You can also use lookup to get from number to color ie color name let colorName: string = Color[2]; // "Blue"
  • any is type that can be used for existing code, it can contain any value and can call any method on it
  • void is only usefull to mark return type of a function (that returns nothing)
  • null and undefined are types for which you can assignly only null and undefined. null and undefined are subtypes of all other types so you can assign null to some :number. But if --strictNullChecks is enabled (default) null can be assignable only to :void or :null. Use union if you don’t know if it will exists number | null.
  • never type represents value that never occur. For example if function always throw exception, it has return type never. it is subtype of all types. And no type is subtype of never (except never)

Type assertions (<_>) are similar to type cast, but has no runtime impact, it’s only used for compiler let length: number = (<string>name).length; or as syntax let length: number = (name as string).length;


Interface describe objects

stao ovde

interface Person {
  firstName: string;
  lastName: string;


class Student {
  fullName: string;
   constructor(public firstName, public middleInitial, public lastName) {
      this.fullName = firstName + " " + middleInitial + " " + lastName;

We can declare and initialize properties, or use variable assigment

class A {
  title: string;
  constructor(public title: string) {
    this.title = title;
  // or simply variable assigment with type anotation
  title: string = title;


Type Hero[] is array of Hero ? optional