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手写promise异步

时间: 2023-02-17 14:29:12 浏览: 38

手写Promise异步的方法如下： ``` // 定义Promise构造函数 function MyPromise(fn) { // 状态机，初始化为pending var state = 'pending'; // 成功结果 var value = null; // 失败原因 var reason = null; // 成功回调函数队列 var successCallback = []; // 失败回调函数队列 var failCallback = []; // resolve方法 function resolve(newValue) { if (state === 'pending') { state = 'fulfilled'; value = newValue; successCallback.forEach(function(cb) { cb(value); }); } } // reject方法 function reject(newReason) { if (state === 'pending') { state = 'rejected'; reason = newReason; failCallback.forEach(function(cb) { cb(reason); }); } } // then方法 this.then = function(onFulfilled, onRejected) { if (state === 'fulfilled') { onFulfilled(value); } if (state === 'rejected') { onRejected(reason); } if (state === 'pending') { successCallback.push(onFulfilled); failCallback.push(onRejected); } } // 执行fn函数 fn(resolve, reject); } ``` 使用方式为: ``` var promise = new MyPromise(function(resolve, reject) { setTimeout(function() { resolve('成功'); }, 1000); }); promise.then(function(value) { console.log(value); }, function(reason) { console.log(reason); }); ``` 这样就实现了一个简单的promise异步.

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