function p1(){    return new Promise(function(resolve,reject){        setTimeout(function(){            console.log("p1_3000");            resolve()        },3000)    })   }function p2(){    return new Promise(function(resolve,reject){        setTimeout(function(){            console.log("p2_2000");            resolve()        },2000)    })}

//await 只能出现在异步函数里 async function f(){    console.log("0000")    await p1();    await p2();    console.log("1010") }  p3=f(); p3.then(function(){     console.log("结束") })

console.log(1);console.log(2);setTimeout(function(){    console.log(3)},3000);console.log(4);console.log(5)

上边的打印结果大家想必都知道，这是同步状态下的执行顺序

//在看一个栗子function p1(){    return new Promise(function(resolve,reject){        setTimeout(function(){            console.log("p1_3000");            resolve()        },3000)    })}function p2(){    return new Promise(function(resolve,reject){        setTimeout(function(){            console.log("p2_2000");            resolve()        },2000)    })}

console.log("0000"); p1(); p2(); console.log("1010") //跟大家预期的结果一样，执行按照如下顺序输出 //0000  //1010 //p2_2000 //p1_3000

咱们想做的是让他按这个顺序执行下来咱们就要用到