generator构造器
function *show(){
yield 12;
yield 5;
}
var gen = show();
console.log(gen.next()); //{value: 12, done: false}
console.log(gen.next()); //{value: 5, done: false}
console.log(gen.next()); //{value: undefined, done: true}
promise
原文：http://www.cnblogs.com/chenweichu/p/6659568.html