Learning TypeScript personal notes

let str: string = 'pawan';

let no:number = 30

let flag: boolean  = true;

let d: null = null;

let e: undefined = undefined;


console.log(no)

console.log(str)



// Array


const cars:string[] = ['a','b','c']

const nums:number[] = [1,2,3,4]

const bool: boolean[] = [true, false];


function printCar(models : string[]){
    models.forEach(element => {
        console.log(element)
    });
}

printCar(cars)


function callIt(model: number | string){
    console.log(model)
}

callIt('true')





// TYPE

type mo = number | string



function printtCar(model: mo){
    console.log(model)
}

printtCar(2)



// Function Type


function pr(cb: Function){
    cb(20,'bmw')
}

type voo = number | string

pr((no : number, str : String )=> console.log(no, str))






// Interfaces
// large scale applications



type Car =  {
    make: string,
    model : string | number,
    sedan: boolean
}

interface Carr  {
    make: string;
    model : string | number;
    sedan: boolean;

    //functions
    accelerate : () => void;
    decellarate() : void;
}


// Objects

function voe(obj_name: {param_a?: string, param_b : number}):void{
console.log(obj_name.param_b)
}

// interface Bv {
//     nm: string
// }

// interface b2 extends By{
//     nm2: number
// }




// Special Types


let car:any = 'bmw'

car = 'honda'
car = true
car = 22



// unknown 

// let a: unknown = document.getElementById('my-element');
// we can throw what ever we want with unknow type


// void
// function returns nothing



// never
function crash(model:number): never{
    throw new Error('car crash')
}
// it doesn't never returns values / anything not even void  maybe kill process | terminate thing 





// Literal types   ( if declared with const )

type Bike = 'NOO' | 123

// const bike: Bike = 'wha';
const bike: Bike = 'NOO';





// Literal interface

const care = {
    make: "honda" as "honda"
}

// care.make = 'mbw'
care.make = 'honda'





// Tuples 

// only last paramater optional allowed

type CARRR = [number | boolean,string?];


// make readonly
type CARRR2 = readonly [number | boolean,string?];

// OR

let cDetails = [2021, 'bmw'] as const;
// cDetails[1] = 'akj';



const ar: CARRR = [1,'2']
console.log('tuples, -> '+ ar)


// maybe use tuple for API calls






// Rest Parameter

type carTuple = [number,string, ...number[]]

const car3 = [2021, 'bmw',23,123,34];


console.log(car3)





// IMPORTANT


// TYPE ASSERTATION    explicility mentioning when don't know

const myCanvar = document.getElementById('canvas') as HTMLCanvasElement;


// NULL ASSERTATION  when you don't have confirmation but sure about values types use -> !
function doSome(model: number | null){
    model!.toString()
}

doSome(null)


// IMPOSSIBLE ASSERTATION

type YO = string | null

const car1 = 'form' as YO;




// IMPORTANT






// export {}