Promise 详情及应用

一.为啥要用Promise?

当方法回调很多很繁琐时，代码嵌套太深，可读性很差，可用Promise

二.概念及用法

Promise  承诺

   //异步
    let isForget = false
    let getPs = new Promise((resolve, reject) => {
        if (isForget) {
            let ps = {
                color: "red",
                price: "$99"
            }
            resolve(ps)
        } else {
            let err = new Error("报错了")
            reject(err)
        }
    })

//基本用法
    let testFn = function() {
        getPs.then((success) => {
            console.log(success)
        }).catch((failure) => {
            console.log(failure)
        })
    }
    testFn()

链式调用

    //异步
    let isForget = true
    let getPs = new Promise((resolve, reject) => {
            if (isForget) {
                let lv = {
                    color: "red",
                    price: "$99"
                }
                resolve(lv)
            } else {
                let err = new Error("wo报错了!!!!")
                reject(err)
            }
        })

    //链式调用

    let getBuyall = (lv) => {
        let cloth = {
            size: "M",
            color: "green"
        }
        let msg = {
            massage: "我的口红yanse：" + lv.color + "我的衣服大小尺寸：" + cloth.size,
            lv: lv,
            cloth: cloth
        }
        return Promise.resolve(msg)
    }


    let testFn = () => {
        getPs
            .then(getBuyall)
            .then((success) => {
                console.log(success)
            }).catch((failure) => {
                console.log(failure.message)
            })
    }
    testFn()