Return parsed output of file from node.js

Question

Return parsed output of file from node.js

I have my file reading in and being parsed properly but I can't seem to return the string of output. I would like to be able to access this string from a variable that it gets assigned to on the client. I'm using async series to help alleviate callback hell and the output hits the console fine. However if I drop return output in that same spot it doesn't work. Suggestions?

embed_analytics: function(){
    var output;

    async.series({
            read_file: function(callback){
               fs.readFile(__rootpath+'/apps/analytics/data/analytics.json', 'UTF-8', function(err,data){
                    if(err) {
                        console.error("Could not open file: %s", err);
                        process.exit(1);
                    }
                    try {
                        var config = JSON.parse(data);
                        callback(null, config);
                    }
                    catch(exception) {
                        console.error("There was an error parsing the json config file: ", exception);
                        process.exit(1);
                    }
                });
            }
        },
        function(err, results) {
            _.each(results.read_file, function(element){
                output+="$('"+element.Selector+"').click(function(){_gaq.push(['_trackEvent',"+element.Category+","+element.Action+","+element.Label+"]);});\n";
            });
            console.log(output);     
        }
    );
}

javascript
node.js
asynchronous
express
fs

Answer 1

returning from an asynchronous function, like the callback for async.series, doesn't mean anything. You'll need to pass a callback into the main function, and call it with output:

embed_analytics: function(final_callback){
  ...
        },
        function(err, results) {
            _.each(results.read_file, function(element){
                output+="$('"+element.Selector+"').click(function(){_gaq.push(['_trackEvent',"+element.Category+","+element.Action+","+element.Label+"]);});\n";
            });
            final_callback(output);     
        }
    );
}

And then use it as you would any other async function:

embed_analytics(function(data) {
  // do something with data
});

Answer 2

It's asynchronous, you CANNOT return something from an asynchronous function. You must accept a callback that gets called when the operation is complete. Brandon Tilley has the correct code to do that.