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