empty array when nesting callbacks

I'm looping over an array of JSON data returned from couchdb, and added the data to an array then returning the array, The array should contain the rows from couchdb but [] is returned.

var Album = {
  all: function() {
    var data, albums = [];
    request({ uri: 'http://127.0.0.1:5984/albums/_all_docs'}, function(error, response, body) {
        if (error) throw error;
        data = JSON.parse(body);
        data.rows.forEach(function(d) {
            request({ uri: 'http://127.0.0.1:5984/albums/' + d.id }, function(error, response, body) {
                if (error) throw error;
                albums.push(JS开发者_如何学GoON.parse(body));  
            });
        });
    });
    return albums;
  }
};

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[] will be returned initially, although once the callback executes the array will contain the necessary data. That's the nature of node's callbacks - they are asynchronous.

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To add to what davin said, you normally handle asynchronous operations with callbacks. The problem with your code is that if you have n different albums, you have n different request operations happening simultaneously but you have no way of knowing when they all finish.

I'm not a Node.js guy, so maybe there are utilities to handle this, but with vanilla javascript, here's how I would handle such a thing with minimal changes to your code.

Here's some pseudo-javascript for brevity

Album.all = function(callback){
    request( "_all_docs", function(albums){
        var albumsLeft = albums.length;
        var results = [];
        albums.forEach( function(album_id){
            request( "albums/" + album_id, function(album){
                results.push(album);
                albumsLeft -= 1;                
                if( albumsLeft === 0){
                    callback(results);
                }
            });
        });
    });
};