浅谈promise中的方法(then、catch、resolve、reject、race、all、done、finally)
https://blog.csdn.net/momdiy/article/details/778560991.then,catchpromise.then(onFulfilled,onRejected)操作之后执行回调函数。Fulfilled为执行成功调用的函数,onRejected为执行失败调用的函数。promise.catch(onRejected)捕获到错误执行onRejected函数3.r