javascript - Backbone.js - Given an element, how do I get the view?

Question

I've created a bunch of Backbone.js views. Each view has an associated element (view.el).

Given an element on the page — out of context of the view — what would be the best way to get the view for the element?

For example, say some event affects a bunch of elements on a page and I want to call a method on every view associated with the affected elements.

One way would be to assign the view to the element's data, but I'm wondering if I've missed something smarter:

var myview = BackBone.View.extend({
    initialize: function(options) {
        $(this.el).data('view', this);
        ...
    }
});

(I'm using Backbone with jQuery 1.5.)

Answer 1

I've just written a jQuery plugin for this. It also uses the .data() method.

Registration:

I have wrapped / proxied the Backbone View setElement method to attach the required data to the view's $el property.

Registration is done behind the scenes like so:

$(myViewsEl).backboneView(myView);

Retrieval:

The plugin traverses up the DOM hierarchy (using .closest()) until it finds an element with the required data entry, i.e a DOM element with an associated view:

var nearestView = $(e.target).backboneView();

In addition, we can specify what type of Backbone View we wish to obtain, continuing up the hierarchy until we find an instance of matching type:

var nearestButtonView = $(e.target).backboneView(ButtonView);

JSFiddle Example:

Can be found here.

Notes:

I hope I am correct in thinking there are no memory leaks involved here; An 'unlink' is performed if setElement is called a second time round, and since removing a view's element calls .remove() by default, which destroys all data as well. Let me know if you think differently.

The plugin code:

(function($) {

    // Proxy the original Backbone.View setElement method:
    // See: http://backbonejs.org/#View-setElement

    var backboneSetElementOriginal = Backbone.View.prototype.setElement;

    Backbone.View.prototype.setElement = function(element) {
        if (this.el != element) {
            $(this.el).backboneView('unlink');                    
        }

        $(element).backboneView(this);    

        return backboneSetElementOriginal.apply(this, arguments);
    };

    // Create a custom selector to search for the presence of a 'backboneView' data entry:
    // This avoids a dependency on a data selector plugin...

    $.expr[':'].backboneView = function(element, intStackIndex, arrProperties, arrNodeStack) {
        return $(element).data('backboneView') !== undefined;        
    };

    // Plugin internal functions:

    var registerViewToElement = function($el, view) {
        $el.data('backboneView', view);
    };

    var getClosestViewFromElement = function($el, viewType) {
        var ret = null;

        viewType = viewType || Backbone.View;

        while ($el.length) {
            $el = $el.closest(':backboneView');
            ret = $el.length ? $el.data('backboneView') : null;

            if (ret instanceof viewType) {
                break;
            }
            else {
                $el = $el.parent();
            }           
        }

        return ret;                
    };

    // Extra methods:

    var methods = {

        unlink: function($el) {
            $el.removeData('backboneView');        
        }

    };

    // Plugin:

    $.fn.backboneView = function() {
        var ret = this;
        var args = Array.prototype.slice.call(arguments, 0);

        if ($.isFunction(methods[args[0]])) {
            methods[args[0]](this);                        
        }
        else if (args[0] && args[0] instanceof Backbone.View) {
            registerViewToElement(this.first(), args[0]);                
        }
        else {
            ret = getClosestViewFromElement(this.first(), args[0]);
        }

        return ret;        
    }        

})(jQuery);