手写Promise A+ 规范

基于es6语法手写promise a+ 规范，源码实现

class promise {
    constructor(excutorcallback) {
        this.status = 'pending';
        this.value = undefined;
        this.fulfilledary = [];
        this.rejectedary = [];

        //=>执行excutor（异常捕获）
        let resolvefn = result => {
            let timer = settimeout(() => {
                cleartimeout(timer);
                if (this.status !== 'pending') return;
                this.status = 'fulfilled';
                this.value = result;
                this.fulfilledary.foreach(item => item(this.value));
            }, 0);
        };
        let rejectfn = reason => {
            let timer = settimeout(() => {
                cleartimeout(timer);
                if (this.status !== 'pending') return;
                this.status = 'rejected';
                this.value = reason;
                this.rejectedary.foreach(item => item(this.value));
            }, 0);
        };
        try {
            excutorcallback(resolvefn, rejectfn);
        } catch (err) {
            //=>有异常信息按照rejected状态处理
            rejectfn(err);
        }
    }

    then(fulfilledcallback, rejectedcallback) {
        //=>处理不传递的状况
        typeof fulfilledcallback !== 'function' ? fulfilledcallback = result => result : null;
        typeof rejectedcallback !== 'function' ? rejectedcallback = reason => {
            throw new error(reason instanceof error ? reason.message : reason);
        } : null;

        //=>返回一个新的promise实例
        return new promise((resolve, reject) => {
            this.fulfilledary.push(() => {
                try {
                    let x = fulfilledcallback(this.value);
                    x instanceof promise ? x.then(resolve, reject) : resolve(x);
                } catch (err) {
                    reject(err);
                }
            });
            this.rejectedary.push(() => {
                try {
                    let x = rejectedcallback(this.value);
                    x instanceof promise ? x.then(resolve, reject) : resolve(x);
                } catch (err) {
                    reject(err);
                }
            });
        });
    }

    catch(rejectedcallback) {
        return this.then(null, rejectedcallback);
    }

    static all(promiseary = []) {//=>promise.all()
        return new promise((resolve, reject) => {
            //=>index:记录成功的数量 result:记录成功的结果
            let index = 0,
                result = [];
            for (let i = 0; i < promiseary.length; i++) {
                //=>promiseary[i]:
                //每一个需要处理的promise实例
                promiseary[i].then(val => {
                    index++;
                    result[i] = val;//=>索引需要和promiseary对应上，保证结果的顺序和数组顺序一致
                    if (index === promiseary.length) {
                        resolve(result);
                    }
                }, reject);
            }
        });
    }
}

module.exports = promise;