自己写一个Promise A+

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自己手动写一个Promise A+代码, 实现了基本功能(包括then/catch/all方法), 代码如下:

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class Promise {
  // constructor
  constructor(executorCallBack) {
    this.status = "pending";
    this.value = undefined;
    this.fulfilledAry = [];
    this.rejectedAry = [];

    let resolveFn = result => {
      let timer = setTimeout(() => {
        clearTimeout(timer);
        if (!this.status === "pending") {
          return;
        }
        this.status = "fulfilled";
        this.value = result;
        this.fulfilledAry.forEach(item => item(this.value));
      }, 0);
    };
    let rejectFn = reason => {
      let timer = setTimeout(() => {
        clearTimeout(timer);
        if (!this.status === "pending") {
          return;
        }
        this.status = "rejected";
        this.value = reason;
        this.fulfilledAry.forEach(item => item(this.value));
      }, 0);
    };

    try {
      executorCallBack(resolveFn, rejectFn);
    } catch (err) {
      rejectFn(err);
    }
  }

  // methods
  then(fulfilledCallBack, rejectedCallBack) {
    typeof fulfilledCallBack !== "function"
      ? (fulfilledCallBack = result => result)
      : null;
    typeof rejectedCallBack !== "function"
      ? (rejectedCallBack = reason => {
          throw new Error(reason instanceof Error ? reason.message : reason);
        })
      : null;
    return new Promise((resolve, reject) => {
      this.fulfilledAry.push(() => {
        try {
          let x = fulfilledCallBack(this.value);
          x instanceof Promise ? x.then(resolve, reject) : resolve(x);
        } catch (err) {
          reject(err);
        }
      });
      this.rejectedAry.push(() => {
        try {
          let x = rejectedCallBack(this.value);
          x instanceof Promise ? x.then(resolve, reject) : resove(x);
        } catch (err) {
          reject(err);
        }
      });
    });
  }

  catch(rejectedCallBack) {
    return this.then(null, rejectedCallBack);
  }

  static all(promiseAry = []) {
    // 用Promise.all() 来执行
    return new Promise((resolve, reject) => {
      let successCounter = 0,
        result = [];
      for (let i = 0; i < promiseAry.length; i++) {
        // promiseAry[i] 每一个处理的promise实例
        promiseAry[i].then(val => {
          successCounter++;
          result[i] = val;
          if (successCounter === promiseAry.length) {
            resolve(result);
          }
        }, reject);
      }
    });
  }
}

module.exports = Promise;