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webVueBlog opened this issue Mar 11, 2020 · 1 comment
Open

26.Promise的简单理解 #26

webVueBlog opened this issue Mar 11, 2020 · 1 comment
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@webVueBlog webVueBlog added the JavaScript JavaScript label Mar 11, 2020
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层面上的理解：

Promise是一个类，有3个状态分别是：等待态（默认） 成功态 失败态

打个比方比如承诺要给女朋友买一个礼物，一开始先承诺下来（等待态），买了（就是成功），你会让她高兴（就是结果），你不买了（就是失败），你的选择会得到不同的结果。

简单体会：

let  promise = new Promise((resolve,reject) => {
    reject('参数')
}).then(data =>{    
//成功
    console.log(data)
},err =>{  
 //失败
    console.log('err',err)
})

每个promise实例都有一个.then方法。resolve（成功）,reject（失败）。
resolve,reject是自己定义的，你需要他成功或者失败，首先要看自己调用的是谁？

（重点）；一旦成功了就不能失败。

如果你手动抛出一个异常那就注定会进失败的结果了。

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