手写Promise

function Promise(executor) {
 // 初始化state为等待态    
 this.state = 'pending';
 // 成功的值
 this.value = undefined;
 // 失败的原因
 this.reason = undefined;
 // 存放 fn1 的回调
 this.fn1Callbacks = [];
 // 存放 fn2 的回调
 this.fn2Callbacks = [];
  // 成功
 let resolve = () => { };
 // 失败
 let reject = () => { };
 // 立即执行
 executor(resolve, reject);
}