<html>
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<head>
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<title>Promise</title>
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<script type='text/javascript'>
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var ok = true;
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function successCallBack(){
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console.log("成功");
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};
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function failureCallBack(){
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console.log("失败");
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};
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function successCallBack1(){
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console.log("成功1");
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return new Promise((resolve,reject) => {
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reject();
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})
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};
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function failureCallBack1(){
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console.log("失败1");
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};
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function successCallBack2(){
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console.log("成功2");
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};
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function failureCallBack2(){
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console.log("失败2");
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};
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const wait = ()=> new Promise((resolve,reject)=> {
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setTimeout(() => {
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console.log('setTimeout执行完毕');
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resolve();
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}, 0);
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});
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const wait2 = ()=> new Promise((resolve,reject)=> {
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resolve();
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setTimeout(() => {
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console.log('setTimeout执行完毕');
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}, 1000);
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});
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//Promise约定与链式调用
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//1.在本轮 事件循环 运行完成之前，回调函数是不会被调用的。以下是个错误示例，resolve回调方法要在setTimeout执行完后在调用。
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var use = wait2().then(successCallBack,failureCallBack);
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//2.即使异步操作已经完成（成功或失败），在这之后通过 then() 添加的回调函数也会被调用。
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var use2 = wait();
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setTimeout(() => {
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use.then(successCallBack,failureCallBack);
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}, 2000);
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//3.通过多次调用 then() 可以添加多个回调函数，它们会按照插入顺序进行执行。一般情况下then会返回一个默认的Promise对象。
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var use3 = wait().then(successCallBack,failureCallBack).then(successCallBack1,failureCallBack1).then(successCallBack2,failureCallBack2);
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</script>
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</head>
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<body>
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</body>
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</html>
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