当我们需要处理多个异步调用时,应该如何处理呢?

//首先假设有2个读取文件的异步调用,promise1和promise2
var promise1 = readFile ("foo.txt", "utf-8");
var promise2 = readFile ("bar.txt", "uft-8");//然后,我们可以使用all()方法将两个单独的Promise重写抽象组合成一个新的Promise,并用then暴露给Deferred
var deferred = new Deferred();
deferred.all([promise1, promise2]).then(function (result) {// 正确情况下做什么
}, function (err) {// 错误了做什么
});// 最后利用prototype重写Deffered的all()方法;
Deferred.prototype.all = function (promises) {var count = promises.length;var that = this;var results = [];promises.forEach(function (promise, i) {promise.then(function (data) {count--;results[i] = data;if (count === 0) {that.resolve(results);}}, function (err) {that.reject(err);});});return this.promise;
};

详情参考《深入浅出NODE》P88