10. Callback
2020. 11. 15. 14:28ㆍJavaScript & TypeScript
- JavaScript is synchronous
- Execute the code block in order after hoisting
- hoisting : var, function declaration
console.log('1');
setTimeout(() => console.log('2'), 1000);
console.log('3');
// 1, 3, 2
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 password');
userStroage.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)});
※출처
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