TypeError：无法调用null的方法“ replace”-Backbone.js

Question

I'm trying to do a tutorial backbone project with peepcode, but I got stuck.

I am trying to render a view from the console by creating a new view from a collection. Here's my code

(function($) {

    window.Album = Backbone.Model.extend({

        isFirstTrack: function(index) {
            return index == 0; 
        },

        isLastTrack: function(index) {
            return index >= this.get('tracks').length - 1; 
        },

        trackUrlAtIndex: function(index) {
            if (this.get('tracks').length >= index) {
                return this.get('tracks')[index].url;
           }
            return null;
        }

    }); 

    window.Albums = Backbone.Collection.extend({
        model: Album,
        url: '/albums'
    });

    window.Album = Backbone.Model.extend({});

    window.AlbumView = Backbone.View.extend({
        tagName: 'li',
        className: 'album',


        initialize: function() {
            _.bindAll(this, 'render');
            this.model.bind('change', this.render);

            this.template = _.template($('#album-template').html());
        },

        render: function() {
            var renderedContent = this.template(this.model.toJSON());
            $(this.el).html(renderedContent);
            return this;
        }
    });

    window.LibraryAlbumView = AlbumView.extend({

    });

    window.LibraryView = Backbone.View.extend({
        tagName: 'section',
        className: 'library',

        initialize: function () {
            _.bindAll(this, 'render');
            this.template = _.template($('#library-template').html());
            this.collection.bind('reset', this.render);
        },

        render: function() {
            var $albums,
                collection = this.collection;

            $(this.el).html(this.template({}));
            $albums = this.$(".albums");
            collection.each(function(album) {
                var view = new LibraryAlbumView({
                    model: album,
                    collection: collection
                });
                $albums.append(view.render().el);
            });
            return this;
        }
    });
})(jQuery);

When I type libraryView = new LibraryView({ collection: library }) In the console I get this response:

TypeError: Cannot call method 'replace' of null

Can anyone help me out?

Answer 1

Most likely the element for the library view doesn't exist in your markup.

This should be true

$('#library-template').length == 1;

This error can happen if you do:

 _.template(null)
 _.template(undefined);

Calling .html() on an element that doesn't exist returns undefined .

Answer 2

What exactly is the library variable (that you're using as the value in the constructor argument to LibraryView ) set to? It's not defined globally, so it's probably null . You'd need to first declare that variable:

var library = new Albums(),
    libraryView = new LibraryView({ collection: library })