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    Using Backbone to improve multiselects

    Sometimes you need to ask a users for multiple answers to a single question. But what's the best way to go about it?


    A multiselect input field is kind of strange for the user, sticks out and doesn't really behave like everything else on the web.

    A bunch of checkboxes is better for the user ... but have you ever tried handling a form with dynamically created checkboxes? Let alone creating useful tests and consolidating everything into a single list of values. No decent forms framework will let you do that easily.

    I had to solve this similar problem for a time and attendance software I worked on, so I made a Javascript thing to convert a select field into a checkbox-field. Then I made it into a simple jquery plugin thing for everyone to use :)

    Check out the demo!

    The idea is pretty simple:

    • take a select, turn it into a list of options
    • every option becomes a Checkbox model in a collection
    • render each Checkbox as a CheckboxView
    • connect everything with some events

    What I really love about the Backbone approach is that all of this works almost magically. Instead of bending over backwards to get checkboxes and the hidden multiselect synced up, all I had to do was create some models, some views and tell them how they are connected.

    This is how the field itself is created

    $multiselect.find("option").each(function (i, el) {
      var $el = $(el);
      // hidden behind the scenes here is that:
      // 1. creating a Checkbox, correctly binds together all needed events
      // 2. adding it to checkboxes, takes care of rendering and adding to the DOM
        new Checkbox({
          value: $el.val(),
          label: $el.html(),
          selected: $el.attr("selected"),

    And to make sure data is synced up between its three representations (multiselect, visual checkboxes, the data structure itself), all it takes is this:

    var Checkbox = Backbone.Model.extend({
      initialize: function () {
        this.bind("change:selected", this.toggled);
        this.attributes.id = this.cid;
      toggled: function () {
        var $opt = $multiselect.find("option[value=" + this.get("value") + "]");
        if (this.get("selected")) {
          $opt.attr("selected", "1");
        } else {

    Yep, that's the whole model and that's all it takes to sync everything up. Pretty cool huh? I remember trying to do this with just jQuery once ... I nearly stabbed my eyes out to end the misery.

    All in all the whole thing is just 123 sloc, which can only mean one thing: Backbone is cool.

    If you use my checkbox-field library, it's only going to be a single sloc for you:


    That's it :)

    Let me know what you think.

    Published on April 13th, 2012 in Checkbox, HTML, JavaScript, jQuery, Languages, Programming, Scripts, Uncategorized, User interface

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