typescript Nested Types code example

Example 1: nested array typescript

interface IThing {
    active: boolean
}

interface IStuff {
    name: string;
    things: IThing[]
}

var blopp: IStuff[] = [
    { name: "aa", things: [{ active: true }, { active: false }] },
    { name: "bb", things: null }];

Example 2: 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.