1 //实现同步操作函数【对time()函数进行实现停顿多长时间n参数传入 实现能够同步执行】
2 console(1);
3 await time(3);
4 console(1);

async function time(n){
    return new Promise(function(resolve, reject) {
        setTimeout(() => {
            resolve();
        }, n);
    })
}

//方法一   【.then()和.catch()分别代表成功与失败回调】
new Promise(function (resolve, reject) {
    setTimeout(() => {
       resolve();//成功执行
       //reject(); 失败执行 一般两者用if与else区分
    }, n);
})
.then(res=>{
   //执行成功的回调即上方resolve() 
})
.catch(err=>{
   //执行成功的回调即上方reject() 
})


//方法二    【在.then中 两参数前为成功回调 后为失败回调】
new Promise(function (resolve, reject) {
    setTimeout(() => {
       resolve();//成功执行
       //reject(); 失败执行 一般两者用if与else区分
    }, n);
})
.then(res=>{
        //成功回调
},err=>{
        //失败回调
})

new Promise(function (resolve, reject) {
    setTimeout(() => {
       resolve();//成功执行
    }, 1000);
})
.then(res=>{
     return new Promise(function (resolve, reject) {
        setTimeout(() => {
           resolve();//成功执行
        }, 1000);
    })
})
.then(res=>{
     return new Promise(function (resolve, reject) {
        setTimeout(() => {
           resolve();//成功执行
        }, 1000);
    })
})

//Promise.resolve()方法
new Promise(function (resolve, reject) {
    setTimeout(() => {
       resolve("res1");//成功执行
    }, 1000);
}).then(res=>{
   console.log("第一次回调结果",res)
   return Promise.resolve(res+" res2")
}).then(res=>{
   console.log("第二次回调结果",res)
   return Promise.resolve(res+" res3")
}).then(res=>{
   console.log("第三次回调结果",res)
})

//直接return字串方法
new Promise(function (resolve, reject) {
    setTimeout(() => {
       resolve("res1");//成功执行
    }, 1000);
}).then(res=>{
   console.log("第一次回调结果",res)
   return res+" res2"
}).then(res=>{
   console.log("第二次回调结果",res)
   return res+" res3"
}).then(res=>{
   console.log("第三次回调结果",res)
})

const p1 = new Promise((resolve, reject) => {
        resolve(‘hello‘);
    }).then(result => result);
const p2 = new Promise((resolve, reject) => {
        throw new Error(‘报错了‘);
    }).then(result => result);
Promise.all([p1, p2])
    .then(result => console.log(result))
    .catch(e => console.log(e));