ES6面试题

1. 下面的输出结果是多少

const promise = new Promise((resolve, reject) => {
console.log(1);
resolve();
console.log(2);
})

promise.then(() => {
console.log(3);
})

console.log(4);

1. 下面Set结构，打印出的size值是多少

let s = new Set();
s.add([1]);
s.add([1]);
console.log(s.size);

1. 下面的代码输出结果是

const promise1 = new Promise((resolve, reject) => {
setTimeout(() => {
resolve(‘success’)
}, 1000)
})
const promise2 = promise1.then(() => {
throw new Error(‘error!!!’)
})

console.log(‘promise1’, promise1)
console.log(‘promise2’, promise2)

setTimeout(() => {
console.log(‘promise1’, promise1)
console.log(‘promise2’, promise2)
}, 2000)

1. 下面代码的运行结果是

const promise = new Promise((resolve, reject) => {
resolve(‘success1’)
reject(‘error’)
resolve(‘success2’)
})

promise
.then((res) => {
console.log(‘then: ‘, res)
})
.catch((err) => {
console.log(‘catch: ‘, err)
})

1. 下面的代码输出结果是多少

Promise.resolve(2)
.then((res) => {
console.log(res)
return 2
})
.catch((err) => {
return 3
})
.then((res) => {
console.log(res)
})

1. 下面的代码输出结果是多少

Promise.resolve()
.then(() => {
return new Error(‘error!!!’)
})
.then((res) => {
console.log(‘then: ‘, res)
})
.catch((err) => {
console.log(‘catch: ‘, err)
})

1. 下面的代码输出结果是多少

Promise.resolve(1)
.then(2)
.then(Promise.resolve(3))
.then(console.log)
8.
const pro1 = new Promise((resolve, reject) => {
throw 1;
})
const pro2 = pro1.then(result => {
return result 2
}, err => {
return err 3;
});
pro1.catch(err => {
return err 2;
})
//pro2类型：Promise对象
//pro2的状态：
pro2.then(result => console.log(result 2), err => console.log(err * 3))

    _//输出：6_<br />_9._