promise.js是Promises的轻量级JavaScript实现。Promises提供了callback-passing的替代方案，异步函数返回一个Promise对象可附加到callbacks中。示例代码：functionasyncfoo(){varp=newpromise.Promise();/*(1)createaPromise*/setTimeout(function(){p.done(null,"Ohai!");/*(3)resolveitwhenready*/},1000);