Promise

Promise基本使用

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//使用resolve和reject来执行异步操作，使用then来接受异步resolve带来的数据
    new Promise((resolve, reject) => {
        //resolve(1 + 1);
        //失败
        reject("error")
    }).then(date => {
        console.log(date)
        //捕获失败
    }).catch(date => {
        console.log(date)
    });
    //第二种写法
    new Promise((resolve, reject) => {
        resolve(2 + 2)
    }).then(data => {
        console.log(data);
    }, error => {
        console.log(error);
    })

Promise链式编程

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//第一种
   new Promise((resolve, reject) => {
       return resolve("saxon")
   }).then(date => {
       console.log("输出=" + date)
       return Promise.resolve(date + " love ")
   }).then(date => {
       console.log("输出2=" + date)
       return Promise.resolve(date + " you ")
   }).then(date => {
       console.log("输出3=" + date)
   })
   //第二种
   new Promise((resolve, reject) => {
       return resolve("saxon")
   }).then(date => {
       console.log("输出=" + date)
       //抛出异常 抛出异常由catch接收，并且下面的方法不会执行
       throw "error message"
       return date + " love "
   }).then(date => {
       console.log("输出2=" + date)
       return date + " you "
   }).then(date => {
       console.log("输出3=" + date)
   }).catch(err => {
       console.log(err);
   })

处理多个请求

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//处理多个请求
    Promise.all([
      //使用多个Promise
        new Promise((resolve, reject) => {
            resolve("saxon")
        }),
        new Promise((resolve, reject) => {
            resolve("love")
        })

    ]).then(date => {
      //接受的数组
        console.log(date)
    })