Backbone/Underscore: How to get index of a model inside render?

Question

I am new to backbone and underscore and I am trying to get model index on render to do some naming inside the template. This post helps find the index on events , Backbone.js: How to get the index of a model in a Backbone Collection?

but how can I find model index on render or initialize ?

  var SectionView = builder.classes.ItemView.extend({

    template: _.template(
        '<div class="pb-item-type-column pb-item custom-section">' +
            '<div class="panel fw-row">' +
                '<div class="panel-left fw-col-xs-6">' +
                    '<div class="column-title">Grid <%- item_index %></div>' +
                '</div>' +
                '<div class="panel-right fw-col-xs-6">' +
                    '<div class="controls">' +
                        '<i class="dashicons dashicons-edit edit-section-options"></i>' +
                        '<i class="dashicons dashicons-admin-page custom-section-clone"></i>' +
                        '<i class="dashicons dashicons-no custom-section-delete"></i>' +
                    '</div>' +
                '</div>' +
            '</div>' +
            '<div class="builder-items"></div>' +
        '</div>'
    ),
     events: {
        'click': 'onSectionWrapperClick',
        'click .edit-section-options': 'openSectionEdit',
        'click .custom-section-clone': 'cloneItem',
        'click .custom-section-delete': 'removeItem',
     },
     initialize: function() {
        this.defaultInitialize();

     },
     render: function() {
        this.defaultRender({

           item_index: 'this is where I need the index'
        });

     },

     cloneItem: function(e) {
        e.stopPropagation();

        var index = this.model.collection.indexOf(this.model),
           attributes = this.model.toJSON(),
           _items = attributes['_items'],
           clonedSection;

        delete attributes['_items'];

        clonedSection = new Section(attributes);
        this.model.collection.add(clonedSection, {
           at: index + 1
        });
        clonedSection.get('_items').reset(_items);

     },

     openSectionEdit: function() {
        this.modal.open();
     },
     removeItem: function() {
        this.remove();

        this.model.collection.remove(this.model);
     },

  });

  var Section = builder.classes.Item.extend({

     defaults: function() {
        var defaults = _.clone(localized.defaults);

        defaults.shortcode = fwThzSectionBuilder.uniqueShortcode(defaults.type + '_');

        return defaults;
     },
     initialize: function() {
        this.defaultInitialize();

        /**
         * get options from wp_localize_script() variable
         */
        this.modalOptions = localized.options;

        this.view = new SectionView({
           id: 'fw-builder-item-' + this.cid,
           model: this
        });

     },

     allowIncomingType: function(type) {
        if (type == 'columns') {
           return true;
        } else {
           return false;
        }
     }

  });

If I could ad least get the parent on render it would help me further but this does not work either

$(this.el).parent();

I am extending this https://github.com/ThemeFuse/Unyson-Builder-Extension/blob/master/includes/option-types/builder/static/js/builder.js

UPDATE AND SOLUTION :

Since this was not my app and I was extending an existing one it was very hard to find my problem. My issue was that app creator has initiated a timeout on initialize and render

https://github.com/ThemeFuse/Unyson-Builder-Extension/blob/master/includes/option-types/builder/static/js/builder.js#L348-L350

thus I was early on collection search.

Morslamina answer and referenced post were both right.

So to you who is looking for index , give your index search some timeout and check. Collection must be there.

Answer 1

Every model that has been assigned to a collection should have an attribute this.collection which references the parent collection. From there, it should be trivial to get the model's index.

render: function(){
    index = this.model.collection.indexOf(this.model)
}

Note that this might get a bit more complicated if you've added your model to multiple collections. In that case, you'll need a reference to the specific collection that you want the index of, because Backbone won't know automagically which collection you're talking about.

EDIT: After looking more closely at your code, I think you have a scoping issue. If you are literally calling

this.defaultRender({
   item_index: this.model.collection.indexOf(this.model)
});

Then this is scoped to your object that you pass to defaultRender, not to the view.

Try instead

index = this.model.collection.indexOf(this.model)
this.defaultRender({
   item_index: index
});