ES6_Promise

Promise:

解决异步回调问题

传统方式使用的话:大部分用回调函数,事件

使用时可以:

<script >let a = 10;// 返回Promise对象let Promis = new Promise(function (resolve, reject) {//resolve 成功的时候调用// reject 失败的时候调用if (a == 10) {resolve('成功');} else {reject('失败');}});
</script>

其中上面的Promis可以接受resolve / reject来进行下一步操作

<script >
//    Promis.then(res=>{//
//    },err=>{//
//    })// 如:Promis.then(res=>{console.log(res);},err=>{console.log(err);})
</script>

使用catch来接收报错:

<script >let a = 10;// 返回Promise对象let Promis = new Promise(function (resolve, reject) {//resolve 成功的时候调用// reject 失败的时候调用if (a == 10) {resolve('成功');} else {reject('失败');}});// reject,发生错误的别名Promis.catch(err => {console.log(err);})
</script>

处理Promise的resolve / reject时,也可以使用 . 连接:

<script >let a = 10;// 返回Promise对象let Promis = new Promise(function (resolve, reject) {//resolve 成功的时候调用// reject 失败的时候调用if (a == 10) {resolve('成功');} else {reject('失败');}});//此处可以直接使用　．连接Promis.then(res => {console.log(res);}).catch(err => {console.log(err);})
</script>

也可以使用then() 来接收resolve / reject 的结果
<script >new Promise().then(res=>{},err=>{})
</script>

将现有东西转成一个promise对象

<script >let a = 10;// 返回Promise对象let Promis = new Promise(function (resolve, reject) {//resolve 成功的时候调用// reject 失败的时候调用if (a == 10) {resolve('成功');} else {reject('失败');}});Promise.resolve('aa'): // 将现有东西转成一个promise对象,resolve状态,成功状态// 等价于:new Promise(resolve => {resolve('aaa')});// 或者:Promise.reject('aaa'): // 将现有东西转成一个promise对象,reject状态,失败状态// 等价于:new Promise(reject => {reject('aaa')});
</script>

promise可以传递状态 resolve / reject:

<script >p1 = new Promise(resolve => {resolve('aaa')});p1.then(res => {console.log(res);})
</script>

Promise.all():

把promise打包,打包完还是一个promise对象

若是其中传入的一个promise对象的状态与其他promise状态不符,会导致报错(必须确保里面所有promise对象都是resolve状态才靠谱)

如:

<script >let p1 = Promise.resolve('aaa');let p2 = Promise.resolve('bbb');let p3 = Promise.resolve('ccc');Promise.all([p1, p2, p3]).then(res => {// console.log(res);let [res1, res2, res3] = res;console.log(res1, res2, res3);})
</script>

Promise.race():

只要用一个成功就返回,如:

<script >let p1 = Promise.resolve('aaa');let p2 = Promise.reject('bbb');let p3 = Promise.resolve('ccc');Promise.race([p1, p2, p3]).then(res => {console.log(res);}).catch(err => {console.log(err);})
</script>

demo_练习:

<script >// 用户登录成功 / 失败 练习let status = 1;let userLogin = (resolve, reject) => {setTimeout(() => {if (status == 1) {resolve({data: '登陆成功', msg: 'asfasfas', token: 'asfyuiofdgb'});} else {reject('失败了');}}, 2000)};let getUserInfo = (resolve, reject) => {setTimeout(() => {if (status == 1) {resolve({data: '获取用户成功', msg: 'asfasfas', token: 'asfyuiofdgb'});} else {reject('失败了');}}, 1000)};new Promise(userLogin).then(res => {console.log('用户登录成功');return new Promise(getUserInfo);}).then(res => {console.log('获取用户信息成功');console.log(res);})
</script>

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