promise函数封装（完整版）

// 声明构造函数
function Promise(executor) {
    // 添加默认属性
    this.PromiseState = 'pending';
    this.PromiseResult = '';
    // 接受多个then链式调用
    this.callbacks = [];
    const self = this;
    // resolve函数
    function resolve(data) {

        if (self.PromiseState !== 'pending') return;
        // 修改对象的状态
        self.PromiseState = 'fulfilled';
        // 设置对象结果的值
        self.PromiseResult = data;
        // 执行成功的回调
        self.callbacks.forEach(item => {
            item.onResolved(data)
        })
    }
    // reject函数
    function reject(data) {
        if (self.PromiseState !== 'pending') return;
        // 修改对象的状态
        self.PromiseState = 'rejected';
        // 设置对象结果的值
        self.PromiseResult = data;
        self.callbacks.forEach(item => {
            item.onRejected(data)
        })
    }
    // 声明执行器函数
    try {
        executor(resolve, reject);
    } catch (e) {
        reject(e)
    }

}
// 添加then方法
Promise.prototype.then = function (onResolved, onRejected) {
    const self = this;
    return new Promise((resolve, reject) => {
        // 封装函数
        function callback(params) {
            try {
                let result = params(self.PromiseResult);
                if (result instanceof Promise) {
                    result.then(v => {
                        resolve(v)
                    }, r => {
                        reject(r)
                    })
                } else {
                    resolve(result)
                }
            } catch (e) {
                reject(e)
            }
        }
        // 调用回调函数
        if (this.PromiseState === 'fulfilled') {
            callback(onResolved)
        }
        if (this.PromiseState === 'rejected') {
            callback(onRejected)
        }
        // 判断pending状态
        if (this.PromiseState === 'pending') {
            // 保存回调函数
            this.callbacks.push({
                onResolved() {
                    callback(onResolved)
                },
                onRejected() {
                   callback(onRejected)
                }
            })
        }
    })
}

let p = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve('ok')
        reject("err")
        // throw "erro
    }, 1000);

})
const res = p.then(value => {
    console.log(value);
    // return "oh yee"
    // throw "error"
}, reason => {
    throw "error"
    // console.warn(reason);
})

console.log(res);