[JavaScript知识库]前端_Promise面试题6

题目一

    Promise.reject(1)
    .then(value => { console.log(value); })
    .then(value => { console.log(value); },
          reason => {
            console.log(`reason1---${reason}`);
          })
    .catch(reason => {
      console.log(`reason2---${reason}`);
    })

结果：reason1---1?

题目二?

    Promise.reject(1)
    .then(value => { console.log(value); })
    .then(value => { console.log(value); },
          reason => {
            console.log(`reason1---${reason}`);
          })
    .then(value => { console.log(value); },
          reason => {
            console.log(`reason2---${reason}`);
          })
    .catch(reason => {
             console.log(`reason3---${reason}`);
          })

题目三?

使用Promise实现每隔1秒输出1,2,3

方法1

    const arr = [1, 2, 3]
    arr.reduce((p, x) => {
      return p.then(() => {
        return new Promise(r => {
          setTimeout(() => {
            r(console.log(x))
          }, 1000);
        })
      })
    }, Promise.resolve())

?方法2?

    const arr = [1, 2, 3]
    arr.reduce((p, x) => p.then(() => new Promise(r => setTimeout(() =>
    r(console.log(x)), 1000))), Promise.resolve())