Question

Suppose I have a CMS application written in Node.js which persists data on a Redis database. When this application creates a new content, it should increment the id counter, add the new id to a list of ides and then set a new hash with content. What I would do for now is to create a function to perform this execution. This function (let us call it createArticle()) would have a callback and would execute the increment. Once the increment was executed, a callback function would push it into the list of ids. After that, another callback would create the hash. The hash-creating callback would call the function passed as parameter to createArticle():

function createArticle(title, content, callback) {
    var client = redis.createClient();
    client.incr("idCounter", function(err, id) {
        if (err) return callback(err, data);
        client.lpush("articleIds", id, function (err, data) {
            if (err) return callback(err, data);
            var key = "article:"+id;
            client.hmset(key, "title", title, "content", content, callback);
        });
    });
}

I would use this function more or less this way (using Express in this example):

app.post('/createarticle', function(req, res) {
    var title = req.body.article.title, 
        content = req.body.article.content;
    createArticle(title, content, function(err, data) {
        if (err) return res.render('error', { status: 500, message: 'Internal Server Error' });
        res.render('index', { status: 200, message: 'Article created!' });
    });
});

However, this code looks a bit cumbersome to me. Is this the way to go. Or is there a better way to do a series of I/O steps? I used Express and Redis in my example, but the answer do not need to use them.

Answer 1

You can make those error-catchers single-lined:

function createArticle(title, content, callback) {
    var client = redis.createClient()
    client.incr("idCounter", function(err, id) {
        if (err) return callback(err, data)
        client.lpush("articleIds", id, function (err, data) {
            if (err) return callback(err, data)
            var key = "article:"+id
            client.hmset(key, "title", title, "content", content", callback)
        })
    })
}

And you could use a helper for handling errors:

function noError(errorCb, cb) {
    var slice = Array.prototype.slice
    return function (err) {
        var currentCb = err ? errorCb : cb
        currentCb.apply(this, slice.apply(arguments, err?0:1)
    }
}

function createArticle(title, content, cb) {
    var client = redis.createClient()
    client.incr("idCounter", noError(cb, function(id) {
        client.lpush("articleIds", id, noError(function (data) {
            var key = "article:"+id
            client.hmset(key, "title", title, "content", content", callback)
        }))
    })
}

Or something like that.