手写promise

面试的笔试题中遇到过手写promise的题目，以下是参考了网上的文章，自己整理的一个简单的promise函数：

function Promise(executor) {
    let self = this;
    self.status = 'pending';
    self.value = 'undefined';
    self.reason = 'undefined';

    function resolve(value) {
        if(self.status === 'pending') {
            self.status = 'resolve';
            self.value = value;
        }
    }

    function reject(reason) {
        if(self.status === 'pending') {
            self.status = 'reject'
            self.reason = reason
        }
    }
    try {
        executor(resolve,reject)
    } catch {
        reject(e)
    }
}

Promise.prototype.then = function (onFulfilled,onRejected) {
    let self = this
    if(self.status === 'resolve') {
        onFulfilled(self.value)
    } else {
        onRejected(slef.reason)
    }
}
module.exports = Promise