题目一 

    Promise.resolve(1)
    .then(
      value => {
        console.log(value);
        return 2
      }
    )
    .then(console.log)

题目二 

    Promise.resolve(1)
    .then(
      value => {
        console.log(value);
        return 2
      }
    )
    .then(
      value => {
        console.log
      }
    )

题目三

    Promise.resolve(1)
    .then(
      value => {
        console.log(value);
        return 2
      }
    )
    .then(
      value => {
        console.log(value)
      }
    )

题目四 

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