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promise源码-class版本【三、Promise源码】【代码详细注释/测试案例完整】

2022-06-27 03:18:00 【翼遥bingo】

JS类和对象后续更博讲解

手撸Promise即完成promise的主要功能
声明构造函数
resolve与reject
throw抛出异常改变状态
Promise的对象状态只能修改一次
then方法执行回调
同步任务回调的执行
异步任务回调的执行
指定多个回调的实现
同步修改状态then方法结果返回
异步修改状态then方法结果返回
Promise的API
构造函数： then，catch

一、 index.html

测试手撸的promise.js

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="./promise.js"></script>
</head>

<body>
    <script> let p = new Promise((resolve, reject) => {
       resolve('OK'); // reject("error"); // throw "err"; setTimeout(() => {
       // resolve('OK'); // reject('err'); // ............................抛出错误该咋办。。。。。。。。。。。。。。 // throw "err"; }, 1000); }); console.log(p); // p.then(value => {
       // console.log(value); // }, reason => {
       // console.warn(reason); // }) const res = p.then(value => {
       // alert(value); return 'hello'; // return new Promise((resolve, reject) => {
       // resolve("success"); // // reject("error"); // }) // throw "fail"; }, reason => {
       alert(reason); }) console.log(res); let res2 = p.catch(reason => {
       console.warn(reason); }) console.log(res2); // 异常穿透，值传递 p.then(value => {
       // console.log(111); // throw '失败了' }).then(value => {
       console.log(222); }).then(value => {
       console.log(333); }).catch(reason => {
       console.warn(reason); }) // resolve方法测试用例 const p1 = Promise.resolve('OK'); const p2 = Promise.resolve(new Promise((resolve, reject) => {
       reject("errpr"); })); const p3 = Promise.resolve(Promise.resolve('Oh Yeah!')); console.log(p1); // reject测试用例 const r1 = Promise.reject('Error'); const r2 = Promise.reject(new Promise((resolve, reject) => {
       resolve('ok') })) console.log(r1); console.log(r2); // 调用all方法 let a1 = new Promise((resolve, reject) => {
       resolve('OK'); }) let a2 = Promise.resolve('Success'); let a3 = Promise.resolve('Oh Yeah'); let result3 = Promise.all([a1, a2, a3]); console.log(result3); // 调用race方法 let ra1 = new Promise((resolve, reject) => {
       setTimeout(() => {
       resolve('OK'); }) }) let ra2 = Promise.reject('Successs'); let ra3 = Promise.resolve('Oh Yeah!') let result4 = Promise.race([ra1, ra2, ra3]); console.log(result4); // then方法回调的异步执行 let then1 = new Promise((resolve, reject) => {
       resolve('OK'); console.log(111); }) then1.then(value => {
       console.log(222); }) console.log(333); </script>
</body>

</html>

二、 promise.js【class版本】

class Promise {
    
    // 构造方法
    constructor(executor) {
    
        // 添加属性
        this.PromiseState = 'pending';
        this.PromiseResult = null;
        // 生命属性
        this.callbacks = [];
        const self = this;

        // resolve函数
        function resolve(data) {
    
            // Promise对象状态只能修改一次
            if (self.PromiseState !== 'pending') return;
            // 1. 修改对象的状态（promiseState）
            self.PromiseState = 'fulfilled';
            // 2. 设置对象结果值（promiseResult）
            self.PromiseResult = data;
            // 调用成功的回调函数
            // if (self.callback.onResolved) {
    
            // self.callback.onResolved(data);
            // }
            setTimeout(() => {
    
                self.callbacks.forEach(item => {
    
                    item.onResolved(item);
                })
            })
        }
        // reject函数
        function reject(data) {
    
            if (self.PromiseState !== 'pending') return;
            self.PromiseState = 'rejected';
            self.PromiseResult = data;
            // 调用失败的回调函数
            // if (self.callback.onRejected) {
    
            // self.callback.onRejected(data);
            // }
            setTimeout(() => {
    
                self.callbacks.forEach(item => {
    
                    item.onRejected(data);
                })
            })
        }

        try {
    
            // 同步调用【执行器函数】
            executor(resolve, reject);
        } catch (e) {
    
            // 修改Promise对象状态为失败
            reject(e);
        }
    }

    // 添加then方法
    then(onResolved, onRejected) {
    
        const self = this;
        // 判断回调函数参数->异常穿透
        if (typeof onRejected !== 'function') {
    
            onRejected = reason => {
    
                throw reason;
            }
        }
        if (typeof onResolved !== 'function') {
    
            onResolved = value => value;
            // value => { return value; }
        }
        return new Promise((resolve, reject) => {
    
            // 封装函数
            function callback(type) {
    
                try {
    
                    // 获取回调函数的执行结果
                    let result = type(self.PromiseResult);
                    // 判断
                    if (result instanceof Promise) {
    
                        // 如果是Promise类型的对象
                        result.then(v => {
    
                            resolve(v);
                        }, r => {
    
                            reject(r);
                        })
                    } else {
    
                        // 结果的对象状态为成功
                        resolve(result);
                    }
                } catch (e) {
    
                    reject(e);
                }
            }
            if (this.PromiseState === 'fulfilled') {
    
                setTimeout(() => {
    
                    callback(onResolved);
                })
            }
            if (this.PromiseState === 'rejected') {
    
                setTimeout(() => {
    
                    callback(onRejected);
                })
            }
            // 判断pending状态
            if (this.PromiseState === 'pending') {
    
                // 保存回调函数
                this.callbacks.push({
    
                    onResolved: function() {
    
                        callback(onResolved);
                    },
                    onRejected: function() {
    
                        callback(onRejected);
                    }
                })
            }
        })

    }


    // 添加 catch方法
    catch (onRejected) {
    
        return this.then(undefined, onRejected);
    }

    // 添加resolve方法【属于类，而不属于实例对象】
    static resolve(value) {
    
        // 返回promise对象
        return new Promise((resolve, reject) => {
    
            if (value instanceof Promise) {
    
                value.then(v => {
    
                    resolve(v);
                }, r => {
    
                    reject(r);
                })
            } else {
    
                resolve(value);
            }
        })
    }


    // 添加reject方法
    static reject(reason) {
    
        return new Promise((resolve, reject) => {
    
            reject(reason);
        })
    }


    // 添加all方法
    static all(promises) {
    
        // 返回结果为promise对象
        return new Promise((resolve, reject) => {
    
            // 声明变量
            let count = 0;
            let arr = [];
            // 遍历
            for (let i = 0; i < promises.length; i++) {
    
                promises[i].then(v => {
    
                    count++;
                    arr[i] = v;
                    if (count === promises.length) {
    
                        // 修改状态
                        resolve(arr);
                    }
                }), r => {
    
                    reject(r);
                }
            }
        })
    }


    // 添加 race 方法
    static race(promises) {
    
        return new Promise((resolve, reject) => {
    
            for (let i = 0; i < promises.length; i++) {
    
                promises[i].then(v => {
    
                    // 修改返回对象的状态为[成功]
                    resolve(v);
                }, r => {
    
                    reject(r);
                })
            }
        })
    }

}