return URLs scraping a webpage with nodejs

Question

I am trying to build a simple web app scraping a website using nodejs and its 2 modules request and cheerio.

I manage to do it with the following code:

    var printURL=function(url){
    request(url, (function() {
        return function(err, resp, body) {
            if (err)
                throw err;
            $ = cheerio.load(body);

            $('img').each(function(){
                console.log($(this).attr('src'));
            });

        }
    } )());
};

It works fine to print the URL of the pictures on the website but what I am really trying to do here is to create a list of url that I could use outside of the function. I tried it this way but it returns an empty list:

var urlList=[];     
var printURL=function(url){
        request(url, (function() {
            return function(err, resp, body) {
                if (err)
                    throw err;
                $ = cheerio.load(body);

                $('img').each(function(){
                    urlList.push($(this).attr('src'));
                });

            }
        } )());
    };

How can I fix this? Many thanks

Answer 1

You need to wait until all callbacks are done.

var urlList=[];     
var printURL=function(url){
    request(url, (function() {
        return function(err, resp, body) {
            if (err)
                throw err;
            $ = cheerio.load(body);
            var images = $('img');
            var counter = images.length;
            images.each(function(){
                urlList.push($(this).attr('src'));
                counter--;
                if (counter==0) {
                    // now we have all images!!
                    console.log(urlList);
                }
            });

        }
    })());
};

This is part of the asynchronous nature of node.js. If things get more complicated I would recommend you to use a flow control library like async.