JS中Promise的类式实现写法

Promise在面试中也会经常遇到，以下是我的手写实现方式，经测试效果不错，小伙伴们们可以直接拷贝使用。

类式定义方式

class MyPromise {
  constructor(executor) {
    this.status = "pending";
    this.value = undefined;
    this.reason = undefined;

    let resolveFn = (value) => {
      if (this.status === "pending") {
        this.status = "resolve";
        this.value = value;
      }
    };

    let rejectFn = (reason) => {
      if (this.status === "pending") {
        this.status = "reject";
        this.reason = reason;
      }
    };

    try {
      executor(resolveFn, rejectFn);
    } catch (error) {
      rejectFn(error);
    }
  }

  then(onFulfilled, onRejected) {
    if (this.status === "resolve") {
      onFulfilled(this.value);
    }
    if (this.status === "reject") {
      onRejected(this.reason);
    }
  }
}

测试和打印

new MyPromise((resolve, reject) => {
  resolve("123");
}).then((res) => {
  console.log(res);
});

输出如下：