手写Promise

function MyPromise(executor) {​
  // 初始化Promise的状态和结果
​  this._state = 'pending';
​  this._value = undefined;​​
  // 回调函数数组，用于存储成功和失败回调
​  this._callbacks = [];​​
  // 定义resolve函数，用于将Promise状态从pending变为fulfilled
  const resolve = (value) => {​
    if (this._state === 'pending') {
​      this._state = 'fulfilled';
​      this._value = value;​
      this._callbacks.forEach(callback => {
​        callback.onFulfilled(value);​
      });​
    }
​  };
​​  // 定义reject函数，用于将Promise状态从pending变为rejected
​  const reject = (reason) => {
​    if (this._state === 'pending') {​
      this._state = 'rejected';
​      this._value = reason;
      this._callbacks.forEach(callback => {
        callback.onRejected(reason);​
      });​
    }
​  };
​​  // 执行executor函数，传入resolve和reject作为参数​
  try {​
    executor(resolve, reject);
​  } catch (error) {
​    reject(error);​
  }​}
MyPromise.prototype.then = function (onFulfilled, onRejected) {
​  if (this._state === 'fulfilled') {​
    onFulfilled(this._value);
​  } else if (this._state === 'rejected') {​
    onRejected(this._value);
​  } else if (this._state === 'pending') {​
    this._callbacks.push({​
      onFulfilled,​
      onRejected,​
    });​
  }​};​​
​​// 示例用法​
const promise = new MyPromise((resolve, reject) => {
​  setTimeout(() => {​    resolve("成功！");​  }, 1000);
​});
​​promise.then(​
  (result) => {​
    console.log("成功：" + result);​
  },
​  (error) => {
​    console.log("失败：" + error);
​  }​);​​​