Node.js回调混淆

Question

我正在尝试使用nowjs在nodejs应用程序上实现一个自动完成程序。

everyone.now.sendAutocomplete = function(search) {  
  var response = getAutocomplete(search);
  console.log("response");
  console.log(response);
};

它调用：

function getAutocomplete(search) {
    console.log(search);
    var artist = new Array();

    request({uri: 'http://musicbrainz.org/ws/2/artist/?query=' + search + '&limit=4', headers: "Musicbrainz Application Version 1"}, function(error, response, body) {
        par.parseString(body, function(err, result) {
            var count = result['artist-list']['@']['count'];

            var artists = result['artist-list']['artist'];
            // var artist = new Array();

            if (count > 1) {
            artists.forEach(function(a) {
                var att = a['@'];
                var id = att['id'];
                var name = a['name'];
                var dis = a['disambiguation'];

                if (dis) {
                    var display = name + " (" + dis + " )";
                } else {
                    display = name;
                }
                artist.push({'id':id, 'name': name, 'disambiguation':dis,
                                     'label':display, 'value':name, 'category':"Artists"});
            });
            //everyone.now.receiveResponse(artist);
            console.log("artist");
            console.log(artist);
            return artist;
        } else {
            console.log(artists);
            var att = artists['@'];
            var id = att['id'];
            var name = artists['name'];
            var dis = artists['disambiguation'];
            var resp = [{'id':id, 'name': name, 'disambiguation':dis,
                                 'label':name, 'value':name, 'category':"Artists"}];
            return resp;
            // everyone.now.receiveResponse([{'id':id, 'name': name, 'disambiguation':dis,
            //                       'label':name, 'value':name, 'category':"Artists"}]);
        }

        });
    });
}

然而，console.log( response )表示该响应是未定义的。我是node的新手，所以答案可能很简单，但仍然无法弄清楚。

Answer 1

您正在将异步调用视为同步调用。您的getAutocomplete需要接受一个回调函数来获取响应。在你的request调用和parseString调用中，你已经用得很多了。

如下所示：

everyone.now.sendAutocomplete = function(search) {  
    getAutocomplete(search, function (response) {
        console.log("response");
        console.log(response);
    });
};

而不是return

function getAutocomplete(search, callback) {
    // ...
    callback(result);
    // ...
}