JS [call back]

'use strict';

// JavaScript is synchronous.

// Excute the coe block by order after hoisting.

// hoisting: var, function declaration

setTimeout(()=> console.log('2'),1000)

// Synchronous callback

    function printImmediately(print){

        print();

    }

printImmediately(()=>console.log('hello'));

// Asynchronous callback

function printWithDelay(print,timeout){

    setTimeout(print,timeout)

}

printWithDelay(()=>console.log('async callback'),2000);

// Callback kHell example

class userStorage{

    loginUser(id,password,onSuccess,OnError){

        setTimeout(()=>{

            if(

                (id==='ellie' && password ==='dream') ||

                (id ==='coder' && password ==='academy')

            ){

                onSuccess(id);

            }

            else{

                OnError(new Error('not found'));

            }

        },2000);

    }

    getRoles(user, onSuccess,OnError){

        setTimeout(()=>{

            if(user==='ellie'){

                onSuccess({name:'ellie',role:'admin'});

            }

            else{

                OnError(new Error('no access'));

            }

        },1000) ;

    }

}

const userStorage =new userStorage();

const id =prompt('enter your id');

const password = prompt('enter your password');

userStorage.loginUser(id,password,

    user=>{

        userStorage.getRoles(user,userWithRole=>{

            alert(`Hello ${userWithRole.name} you have a ${userWithRole.role} role`)

        },error=>console.log(error))

    },error=>{console.log(error);});