typeof typescript code example

Example 1: typescript check type of variable

if (fooOrBar instanceof Foo){
  // TypeScript now knows that `fooOrBar` is `Foo`
}

Example 2: typescript check type

mySprite instanceof Sprite;

Example 3: use type as value typescript

Typescript interfaces aren''t being compiled into the js output, and you can not use them at runtime

Example 4: custom types in typescript

// simple type
type Websites = 'www.google.com' | 'reddit.com';
let mySite: Websites = 'www.google.com' //pass
//or
let mySite: Website = 'www.yahoo.com' //error
// the above line will show error because Website type will only accept 2 strings either 'www.google.com' or 'reddit.com'.
// another example. 
type Details = { id: number, name: string, age: number };
let student: Details = { id: 803, name: 'Max', age: 13 }; // pass
//or 
let student: Details = { id: 803, name: 'Max', age: 13, address: 'Delhi' } // error
// the above line will show error because 'address' property is not assignable for Details type variables.
//or
let student: Details = { id: 803, name: 'Max', age: '13' }; // error
// the above line will show error because string value can't be assign to the age value, only numbers.

Example 5: typeof javascript

console.log(typeof 'blubber');

Example 6: typing in typescript

var name: string = "Anna";
let notes: (number | string)[] = ["Get Food", 23, "Call the previous number when betting"];