# 搜尽全网，整理了19道promise 面试题，你能做对几个？

PS:下面题目没有附答案，有了答案想必会降低大家的思考深度，起不到什么效果，完整答案会在后面文章单独发出。

# 主要考察点

执行顺序
值透传
错误处理
返回值
链式调用

最终考察的还是我们对promise的理解程度。

# 目标

通关标准，能够给出答案，并且给出合理的解释。【为什么给出这个答案？】

# #01

难易程度：⭐⭐⭐

Promise.resolve(1)
  .then((res) => {
    console.log(res)
    return 2
  })
  .catch((err) => {
    return 3
  })
  .then((res) => {
    console.log(res)
  })

# #02

难易程度：⭐

const promise = new Promise((resolve, reject) => {
    console.log(1)
    resolve()
    console.log(2)
})
promise.then(() => {
    console.log(3)
})
console.log(4)

# #03

难易程度：⭐⭐⭐

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)

# #04

难易程度：⭐⭐

setTimeout(()=> console.log(5), 0);
new Promise(resolve => {
    console.log(1);
    resolve(3);
    Promise.resolve().then(()=> console.log(4))
}).then(num => {
    console.log(num)
});
console.log(2);

# #05

难易程度：⭐⭐

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)
  })

# #05

难易程度：⭐⭐

const promise = new Promise((resolve, reject) => {
  setTimeout(() => {
    console.log('once')
    resolve('success')
  }, 1000)
})

const start = Date.now()
promise.then((res) => {
  console.log(res, Date.now() - start)
})
promise.then((res) => {
  console.log(res, Date.now() - start)
})

# #06

难易程度：⭐⭐⭐

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

# #07

难易程度：⭐⭐⭐⭐

const promise = Promise.resolve()
  .then(() => {
    return promise
  })
promise.catch(console.error)

# #08

难易程度：⭐⭐⭐

Promise.resolve(1)
  .then(2)
  .then(Promise.resolve(3))
  .then(console.log)

# #09

难易程度：⭐⭐⭐

Promise.resolve()
  .then(function success (res) {
    throw new Error('error')
  }, function fail1 (e) {
    console.error('fail1: ', e)
  })
  .catch(function fail2 (e) {
    console.error('fail2: ', e)
  })

变种后

Promise.resolve()
  .then(function success1 (res) {
    throw new Error('error')
  }, function fail1 (e) {
    console.error('fail1: ', e)
  })
  .then(function success2 (res) {
  }, function fail2 (e) {
    console.error('fail2: ', e)
  })

# #10

难易程度：⭐⭐⭐⭐

process.nextTick(() => {
  console.log('nextTick')
})
Promise.resolve()
  .then(() => {
    console.log('then')
  })
setImmediate(() => {
  console.log('setImmediate')
})
console.log('end')

# #11

难易程度：⭐⭐⭐⭐

const first = () => (new Promise((resolve, reject) => {
    console.log(3);
    let p = new Promise((resolve, reject) => {
        console.log(7);
        setTimeout(() => {
            console.log(5);
            resolve(6);
        }, 0)
        resolve(1);
    });
    resolve(2);
    p.then((arg) => {
        console.log(arg);
    });

}));

first().then((arg) => {
    console.log(arg);
});
console.log(4);

# #12

难易程度：⭐⭐

var p = new Promise((resolve, reject) => {
  reject(Error('The Fails!'))
})
p.catch(error => console.log(error.message))
p.catch(error => console.log(error.message))

# #13

难易程度：⭐⭐⭐

var p = new Promise((resolve, reject) => {
  return Promise.reject(Error('The Fails!'))
})
p.catch(error => console.log(error.message))
p.catch(error => console.log(error.message))

# #14

难易程度：⭐⭐

var p = new Promise((resolve, reject) => {
    reject(Error('The Fails!'))
  })
  .catch(error => console.log(error))
  .then(error => console.log(error))

# #15

难易程度：⭐⭐

new Promise((resolve, reject) => {
    resolve('Success!')
  })
  .then(() => {
    throw Error('Oh noes!')
  })
  .catch(error => {
    return "actually, that worked"
  })
  .catch(error => console.log(error.message))

# #16

难易程度：⭐⭐

Promise.resolve('Success!')
  .then(data => {
    return data.toUpperCase()
  })
  .then(data => {
    console.log(data)
    return data
  })
  .then(console.log)

# #17

难易程度：⭐⭐

Promise.resolve('Success!')
  .then(() => {
    throw Error('Oh noes!')
  })
  .catch(error => {
    return 'actually, that worked'
  })
  .then(data => {
    throw Error('The fails!')
  })
  .catch(error => console.log(error.message))

# #18

难易程度：⭐⭐⭐⭐

const first = () => (new Promise((resolve,reject)=>{
    console.log(3);
    let p = new Promise((resolve, reject)=>{
         console.log(7);
        setTimeout(()=>{
           console.log(5);
           resolve(6); 
        },0)
        resolve(1);
    }); 
    resolve(2);
    p.then((arg)=>{
        console.log(arg);
    });

}));

first().then((arg)=>{
    console.log(arg);
});
console.log(4);

# #19

难易程度：⭐⭐⭐⭐⭐

async function async1() {
  console.log(1);
  const result = await async2();
  console.log(3);
}

async function async2() {
  console.log(2);
}

Promise.resolve().then(() => {
  console.log(4);
});

setTimeout(() => {
  console.log(5);
});

async1();
console.log(6);

#

# # 最后

以上19个代码题未贴答案，后面会单独发送。

也欢迎大家在留言区回复参与答题。

今天一提就到这里，希望对你有所帮助。

参考资料:

https://zhuanlan.zhihu.com/p/34421918

https://zhuanlan.zhihu.com/p/30797777

https://zhuanlan.zhihu.com/p/98164787

https://juejin.cn/post/6844903986210816013#heading-3

https://juejin.cn/post/6844903605250572302

← 目录 Promise →