Promise 及其它 一个不错的解说

http://www.qingpingshan.com/jb/javascript/180607.html

   <script>
        var flag = true
        var myPromise = new Promise(function(resolve,reject){
            if(flag)
                resolve('ok')
            else
                reject('no')
        })

        var nextPromise = function(prevValue){
            console.log(prevValue)
            return Promise.resolve({ok:1,v:prevValue})
        }

        myPromise
        .then(nextPromise)
        .then(function(value){
            console.log(value)
        })
        .catch(function(error){
            console.error(error)
        })



    </script>

加入箭头函数后:

   <script>
        let flag = true
        const myPromise = new Promise((resolve,reject)=>{
            if(flag)
                resolve('ok')
            else
                reject('no')
        })

        const nextPromise = prevValue =>{
            console.log(prevValue)
            return Promise.resolve({ok:1,v:prevValue})
        }

        myPromise
        .then(nextPromise)
        .then(value => 
            console.log(value)
        )
        .catch(error =>
            console.error(error)
        )
    </script>

ES7 async 函数版:

<script>

    const myPromise = new Promise((resolve, reject) => {
        let backValue = true

        //模拟一个异步耗时操作
        setTimeout(()=>{
            if(backValue)
                resolve({code:'OK',value:1})
            else
                reject(new Error('SOME WORONG HAS HAPPEND!'))
        },2000)
    })


    async function nextPromise(prevValue) {
        console.log(prevValue)
        return Promise.resolve({ ok: 1, v: prevValue })
    }

    async function execute() {
        try {
            //注意await 必须在async 函数里面使用
            let prevValue = await myPromise
            let nextValue = await nextPromise(prevValue)

            console.log(nextValue)

        } catch (error) {
            console.log(error)
        }

    }
    execute()

</script>