Question

I’m learning Backbone.js and am trying to figure out whether it’s possible to have instance variables in Backbone views.

My goal is to load a view’s templates from an external file when a view is being instantiated. Currently I’m storing them in a global variable in the Backbone app’s global namespace, but it would be cleaner to store the templates in a view’s instance variables. Currently I have it set up like this:

var templates = {};

MessageView = Backbone.View.extend({

    initialize: function() {
        $.get('js/Test2Templates.tpl', function(doc) {

            var tmpls = $(doc).filter('template');

            templates['MessageView'] = [];

            tmpls.each(function() {
                templates.MessageView[this.id] = $.jqotec($.unescapeHTML(this.innerHTML));
            });
        });
    },

    render: function() {
        var tpldata = {name: 'Ville', thing: 'Finland'};
        $('#display').jqoteapp(templates.MessageView.greeting_template, tpldata);
    },

    events: {
        "click input[type=button]": "additionalTransactions"
    },

    additionalTransactions: function() {
        this.render();
    }

});

But instead of using “templates” being defined as a global var, I’d like to create ‘templates’ in a view’s initialize function, along these lines (but this doesn’t work):

MessageView = Backbone.View.extend({

    view_templates: {},

    initialize: function() {
        $.get('js/Test2Templates.tpl', function(doc) {

            var tmpls = $(doc).filter('template');

            tmpls.each(function() {
                this.view_templates[this.id] = $.jqotec($.unescapeHTML(this.innerHTML));
            });
        });
    },

    render: function() {
        var tpldata = {name: 'Ville', thing: 'Suomi'};
        $('#display').jqoteapp(this.view_templates.greeting_template, tpldata);
    },

    events: {
        "click input[type=button]": "additionalTransactions"
    },

    additionalTransactions: function() {
        this.render();
    }

});

This is probably (?) pretty straightforward and/or obvious, but me being somewhere on the Backbone.js learning curve, I’d much appreciate any help with this!! Thanks!

Answer 1

Your view_templates instance variable is fine (and a good idea as well). You just have to be sure that you’re using the right this inside your $.get() callback and inside your tmpls.each() call. I think you want your initialize to look more like this:

initialize: function() {
    this.view_templates = { };

    var _this = this;
    $.get('js/Test2Templates.tpl', function(doc) {
        var tmpls = $(doc).filter('template');
        tmpls.each(function() {
            _this.view_templates[this.id] = $.jqotec($.unescapeHTML(this.innerHTML));
        });
    });
},

I’m not sure which this.id you want inside the tmpls.each() but I’m guessing that you want the DOM id attribute from the current template so I left it as this.id.

The this.view_templates assignment in your constructor (initialize) is needed because you presumably want each instance of the view to have its own copy of the array. Creating a new view instance doesn’t do a deep copy of the the view so if you just have:

MessageView = Backbone.View.extend({
    view_templates: {},
    // ...

then all the instances will end up sharing the same view_templates object and view_templates will behave more like a class variable than an instance variable.

You can specify your instance variables in the view definition (i.e. the Backbone.View.extend() call) as a form of documentation but you will want to initialize any of them that should behave as an instance variable in your initialize method; read-only or “class variables” like events can be left as part of the view’s definition.