Pormise 的简单的实例

console.log('here wo go')
new Promise(resolve=>{
    setTimeout(()=>{
       resolve('hello');
    },2000)
})
  .then(value=>{
       console.log(value + 'world')
  })

实例2

console.log('here wo go')
new Promise(resolve=>{
    setTimeout(()=>{
       resolve('hello');
    },2000)
})
  .then(value=>{
       console.log(value)
       return new Promise(resolve=>{
                 setTimeout(()=>{
                    resolve('world');
                 },2000)
              })
  })
  .then(value=>{
     console.log(value+ "world")
   })


// here we go

// hello

// world world