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'use strict';

// JavaScript is synchronous.

// Execute the code block by orger after hoisting.

// hoisting: var, function declaration

console.log('1');

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

console.log('3');

// 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 Hell 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 passrod');

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);

}

);