#jQuery

Recently I was working on a project which was using the jQuery File Upload Plugin to do multiple file uploads. I needed to show the progress of each upload (in this case just images). Looking through their documentation it shows how to a few ways to do custom templates. By default it uses the Javascript Templates Engine for all of its templating. I wanted to use just a div on the page for my template. Here’s how I ended up doing it.

First My basic markup for the html:

Basically my “#template” div was a hidden div on the page which I used as the photo being uploaded. Now for the javascript:

It ended up being pretty simple and self explanatory. The ‘progress’ function is called each time there is a progress update. You can do more advanced templates using their templating engine, however as I was adapting the code to an existing layout and was on a time constraint this was the route I took.

Hope this saves you sometime if you are looking to just quickly add a progress template for the uploaded images.

Posted In: Demo, jQuery

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I was working on a BackboneJS project recently that was using UnderscoreJS for templating and started wondering if its possible to invoke UnderscoreJS recursively.

At face value, the _.template function simply takes a template string and converts it to a first class Javascript function so I figured it would be possible. Out of curiosity, I decided to take a look at how the _. function is actually implemented:

Not any real surprises there – it basically does a series of string replaces on the template you pass in to interpolate any variables you want outputted, converts blocks you want evaluated to regular Javascript, and then injects the object you passed in into the local scope.

Then, the “magic” happens at “var render = new Function(settings.variable || ‘obj’, ‘_’, source);” where a new function is created with a “print” function locally defined and your template converted to a Javascript function.

Here is the “source” string that is passed into “new Function”:

That is the dynamic function generated for the following template:

Since its looking for the “template” function in the global scope it looks like everything should work fine. To test it, I decide to take the Fibonacci sequence and generate boxes for each of the numbers in the sequence up to some N.

Theres a live demo running at http://twitlabs.net/us/ and a Gist of the code is replicated below:

Just for fun, you can also change how the boxes are arranged by toggling between “Stacked” and “Cascaded”.

Anyway, fair warning – I imagine there are some performance implications regarding doing this as well as computational limits. You could potentially cause a stack overflow by consuming your entire stack via the recursion.

As always, questions, comments, concerns welcome!

Posted In: BackboneJS, Demo

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We’ve recently started using BackboneJS on a couple of projects to help create more responsive UIs and avoid having to deal with a tangled mess of jQuery callbacks, ad-hoc Javascript templating, and difficult code re-use. On the whole, I’ve been impressed with Backbone and I think it’ll make a valuable asset in our toolbox.

Anyway, one of the core concepts of Backbone is that client side models will be automatically synced with their server side counterparts via RESTful AJAX calls. Stripping away the buzzword bingo, what that means is that when a Backbone model is created in the UI a AJAX POST request is initiated to create that model, updates trigger a PUT, and destroying a model will cause a DELETE.

Conceptually, this system makes a lot of sense and it fits nicely with how data is structured in most apps. Unfortunately, it falls apart when there isn’t a one to one correspondence between frontend Backbone models and your backend persistence layer.

For example, say on the frontend you wanted to allow a user to enter and edit the various languages she spoke. Naturally, you could define a Backbone “Language” model, managed by a “LanguageList” Collection, and finally drawn with a “LanguageView” View. This would work great but unfortunately on the backend you’re storing the list of languages the user speaks in a single row – say as a CSV list for arguments sake. At this point, you’d be stuck because Backbone would be pushing AJAX requests per model and your backend would have no way to combine the languages into a CSV list.

In this instance it seems like you really want “JSON over REST”, in the sense that you want to push update events for several models on a single request. The Backbone FAQ mentions this technique but unfortunately doesn’t elaborate on specifically how to achieve this behavior.

Batch operations on Models are common, but often best handled differently depending on your server-side setup. Some folks don’t mind making individual Ajax requests. Others create explicit resources for RESTful batch operations: /notes/batch/destroy?ids=1,2,3,4. Others tunnel REST over JSON, with the creation of “changeset” requests:

Google’ing around I stumbled across this StackOverflow answer – http://stackoverflow.com/questions/11298152/how-to-do-batch-operations-in-backbone-js-via-tunneling-rest-over-json which seems to have been removed. The answer basically suggested embedding a Collection within a Model so that Backbone effectively passed a JSON array to your REST endpoint.

Unfortunately, the answer didn’t provide a concrete example either so here is a stripped down version of what I ended up using.

Basically, “Language” is the “real” model which is managed by the “LanguageList” collection. Then, “LanguageCollection” is the container model which holds a single “LanguageList” collection and is subsequently managed by the “LanguageCollectionList”.

If you look through the code, basically the Views are bound to events on ‘LanguagesCollection.at(0).get(“languages”)’ which is a LanguageList object.

The other thing to note is that Language.destroy() function is updated to not make an AJAX DELETE call but instead trigger a save on the collection.

Also, LanguageCollection.parse() is defined as an empty function because ‘LanguagesCollection.at(0).get(“languages”)’ needs to remain a Backbone object and not be converted into the regular JSON which would come back from the server. The caveat here is that if you need to set an ID after a POST, you’ll need to update parse() to process the JSON and then update the corresponding models within the collection.

Anyway, I’m still a Backbone novice so any input or insight is more than welcome. I’d also love to know if theres a more straightforward way to address this. A couple of posts mentioned overriding Backbone.sync but that wasn’t feasible for me because I had other Backbone models on the page which needed to update using the regular REST pattern.

Update 7/20/2012

As pointed out by Aria below, it’s actually possible to override the “sync” method per model to achieve this JSON over REST behavior. Overall, its probably a cleaner solution since it avoids introducing the complexity of collections contained in models simply to get the JSON over REST behavior.

Here’s an example implementation of a sync function that produces the desired results:

NOTE: Almost all of that code is copied directly out of Backbone.js, the exception is the following block which collects up all the models in the current model’s collection and then adds it into the “data” field:

Happy Backbone’ing!

Posted In: BackboneJS, Demo

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You’re all probably familiar with the UI convention of allowing users to select ALL or NONE for a list of checkboxes (like in Gmail). Recently I was working on a project that had a large table full of checkboxes (imagine a 10×10 grid) where the user would need to toggle some but not all of the checkboxes in a given row. And to make matters more complex, they would need to toggle groups of non-consecutive checkboxes (say 15, skip 10, 5, etc.). I threw on the thinking cap but couldn’t think of any similar interactions I’d seen and couldn’t think of a particularly good way to achieve this.

Enter jQuery UI. I happened to stumble across the jQuery UI Selectable documentation and realized it would provide a good UI experience to toggle some but not all of the checkboxes. The code to implement this is surprisingly simple:

Note: You don’t actually need the div container – that was just for JSFiddle.

And then the Javascript (jQuery + jQuery UI):

You can check out a live demo at http://jsfiddle.net/whMyQ/3/

As always, questions and comments are welcome!

Posted In: Demo, jQuery

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A few days ago I was working on a project for a client that basically involved allowing a non-technical end user to build arbitrarily complex boolean queries using a UI. The user could basically click, configure, and drag/drop queries to build expressions like (A AND B OR C) AND (Z OR X). They would also need the ability to edit the pieces in-line, toggle ANDs to ORs, and so on.

Anyway, not to difficult to represent with a data structure but the complexity was going to be in tying the UI to the data structure with callbacks and events. Usually, I would of used a single $(“a”).click() handler to handle all the edit, delete, and configuration clicks in the UI but that quickly devolves into a disastrous mess of if statements and hasClass() checks.

Hoping to avoid this, I started thinking about cleaner ways to implement this and realized if I actually bound events to the individual objects they were going to effect the resulting code would be much cleaner. The UI elements were going to be dynamically generated each time the data structure was updated anyway so binding $.click() events on the <a> tags to their corresponding objects wouldn’t be to much extra work.

All in all, things worked out pretty well. The final code is much easier to follow and there isn’t a gigantic if() block which is impossible to trace.

I can’t share the actual implementation I used but I threw together an example which outlines the technique. Check out the JSFiddle at http://jsfiddle.net/fN46q/4/

Looking at the code, the Board object is an Array that in turn contains Piece objects to form a 3×3 grid.

The Piece objects individually supply a render function to display themselves and then contain a click() function which handles their $.click() events.

The key line which makes this work is:

   $(td).find("a").bind("click", {piece: this[i][j]}, this[i][j].click);

What the second parameter does is add the object into the Event object that is passed to the event handler. More info is available on the $.bind() documentation but looking at the click() function in the Piece object you can see where it comes in to play:

 click: function( e ){
    e.data.piece.val = !e.data.piece.val;
    e.data.piece.board.render();
    return false;
 }

So effectively, the data structure is now linked to the DOM.

As always, thoughts, comments and are feedback welcome!

Posted In: Demo, jQuery

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