在node.js中同步调用

Question

我有以下方法：

var get = function(query_para,callback) {

    var queryParams = query_para;
    var timestamp ;
    var some_Data = {};
    var data;

    request({url:"http://some-url.com/q?", qs:queryParams}, function(err, response, body) {
        if(err) { console.log(err); return; }
        console.log(body);
        var data = JSON.parse(body);

        some_Data.count = data.count; 

        console.log("Returned data: "+some_Data.count);

         callback(null,some_Data);
    });

};

我想把这个方法调用两次，并结合它们的结果。我通过以下方式使用回调实现了它：

get({ start: '2014/09/13-10:00:00', end: '2014/09/13-11:00:00', format: 'json' }, function(err, result1){
    get({ start: '2014/09/13-11:00:00', end: '2014/09/13-12:00:00', format: 'json' }, function(err, result2){
        console.log("r1:: "+result1.count);
        console.log("r2:: "+result2.count);
    });
});

有什么更好的方法让它同步吗？我读到了一些东西(承诺和同步客户端)，但我不明白。怎样才能两次调用该函数并结合它们的结果？

Answer 1

首先，看起来您的代码并不是同步的。我建议让它保持异步，并使用像Q这样的承诺库。首先，确保安装了Q：

npm install q

从您的get函数中返回一个承诺：

var get = function(query_para) {

    var queryParams = query_para;
    var timestamp ;
    var some_Data = {};
    var data;
    //Use q
    var Q = require("q");

    //define a deferred that will be resolved later
    var deferred = Q.defer();

    request({url:"http://some-url.com/q?", qs:queryParams}, function(err, response, body) {
        if(err) { console.log(err); return; }
        console.log(body);
        var data = JSON.parse(body);

        some_Data.count = data.count; 

        console.log("Returned data: "+some_Data.count);

        //resolve the deferred here
        deferred.resolve(some_Data);
    });

    //return the promise
    return deferred.promise;
};

从调用get函数的代码中：

var q = require("q");
var promiseArr = [];
//First promise to your get function
promiseArr.push(get({ start: '2014/09/13-10:00:00', end: '2014/09/13-11:00:00', format: 'json'}));
//Second promise
promiseArr.push(get({ start: '2014/09/13-11:00:00', end: '2014/09/13-12:00:00', format: 'json' }));

//Use q.all to call a callback when all promises in the array are resolved:
q.all(promiseArr).then(function (results) {
   //First item is the data resolved from the first promise in the array
   console.log("r1:: "+results[0].count);
   //Second item is data resolved from second promise
   console.log("r2:: "+results[1].count);
});