一般写法：

  new Promise((resolve,reject) => {
    setTimeout(() => {
      resolve()
      reject()
    }, 1000)
  }).then(
    console.log("Hello Promise")
  ).catch(() =>{
    console.log('error')
  })

简易的then写法：

传输数据时的原始写法：

  new Promise((resolve, reject) =>{
    setTimeout(() => {
      console.log('1')
      resolve('1')
    }, 1000)
  }).then((data) =>{
    console.log(data + '1')

    return new Promise((resolve,reject) => {
      setTimeout(() => {
        resolve(data + '1')
      },1000)
    })
  }).then((data) =>{
    console.log(data + '1')

    return new Promise((resolve,reject) => {
      setTimeout(() => {
        resolve(data + '1')
      },1000)
    })
  })

传输数据时的简易写法：

 Promise.all的写法;(应用场景在于需求建立在多次请求后）

  Promise.all([ 
    new Promise((resolve,reject) => {
      setTimeout(() =>{
        resolve('demo1')
      },1000)
    }),
    new Promise((resolve,reject) => {
      setTimeout(() =>{
        resolve('demo2')
      },1000)
    })
  ]).then(results => {
    console.log(results)
  })

（请求了demo1和demo2数据后一起进行打印)