Creating A Modal Dialog In A Backbone.js Kind Of Way

December 14th, 2011 by Gareth / Comments

I’m finally using Backbone.js. It’s brilliant and I can’t recommend it enough. Backbone is not trivial but it solves a difficult problem.

So I needed a modal dialog. I messed about with a couple of modal dialog plugins but had problems getting them to work in a way that fits in with Backbone.js. After finding out how easy it is to create your own modal dialogs I decided to create a new Backbone.js view from which other views can derive and inherit modal functionality.

You can download a demo of my Backbone modal view from my Github page which looks like this :

The demo doubles as a basic demonstration of Backbone.js and of my modal view. When you click “Add another person to the list” a Backbone view is created which derives from ModalView. This gives the child Backbone view a showModal() method. You just render your view as normal and then call showModal(). For example here is the click handler for the add person button :

   function( event) {
      // Create the modal view
      var view = new AddPersonView();
         x: event.pageX,
         y: event.pageY

The AddPersonView class extends my ModalView class like this :

	AddPersonView = ModalView.extend({
    name: "AddPersonView",
    model: PersonModel,
        "<form>" +
 "<label for="personName">Person's name</label>" +
 "<input id="personName" type="text" />" +
 "<input id="addPersonButton" type="submit" value="Add person" />" +
    initialize:function() {
      _.bindAll( this, "render");
      this.template = _.template( this.templateHtml);
    events: {
      "submit form": "addPerson"
    addPerson: function() {
      _people.add( new PersonModel({name: $("#personName").val()}));
    render: function() {
		$(this.el).html( this.template());
		return this;

Because AddPersonView extends ModalView you can call showModal() on your view and this happens :

What you’re seeing is the el property of the AddPersonView instance being rendered into a modal container which gives you a few things for free :

  • You can close the dialog by either pressing escape, clicking outside of the dialog or pressing the close icon
  • The background is shaded back to highlight the modal view
  • The focus is automatically set on the first form control in the modal view
  • The modal dialog is, by default, positioned in the centre of the screen

In this example I’m positioning the dialog at the mouse cursor coordinates at the point when you click the “Add another person to the list” button. You can pass an options object to showModal() which gives you a bit of control of the internals of the modal dialog code. Here are the defaults that you can override :

	defaultOptions: {
	closeImageUrl: "close-modal.png",
	closeImageHoverUrl: "close-modal-hover.png",

And as you have seen you can also pass in x and y properties. Hopefully these options are self explanatory except perhaps bodyOverflowHidden which helps the dialog stay on screen. The new Twitter add new tweet dialog does something like this too.

The demo includes two images that represent the close button and its hover state (it goes red when you hover over it). You can override the images easily through the showModal() parameter.

Back to the demo

If you type a name in and press the Add person button then a person model is added to the person collection. Because this is Backbone.js this automatically triggers the rendering of a new PersonItemView into the PersonListView :

I’m Happy

I’m happy I stepped back and learned javascript properly and got into Backbone.js. I find that being self critical and determined makes you a better developer. Backbone.js forces you to break your UI down into small units and collections of units, each with their own set of event handlers. And it forces you to do this before you start creating your UI. This is crucial because it enforces design and forethought, the absence of which normally leads to big balls of code mud.

To learn Backbone.js I found the following resources useful :

Finally I know that modal dialogs are known to be not in the best interests of usability but there is a subtle difference between true I-want-to-take-over-your-app-and-secretly-own-the-whole-world modal dialogs and these soft easily-closed dialogs. Facebook uses soft dialogs, as does Twitter. Use inline editing where it makes sense and a separate page where a modal dialog is being asked to do too much.

Download the code and demo from github or see the demo page live in action

Update: v0.3 is complete adding a few new features I needed.

Javascript, UI

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