问Backbone.js:使用RESTful API时视图不会呈现

EN

<div id="js-spa-container"></div>

var Post = Backbone.Model.extend();

var Posts = Backbone.Collection.extend({

    model: Post,

    url: 'https://jsonplaceholder.typicode.com/posts',

    initialize: function(){
        this.fetch({
            success: this.fetchSuccess,
            error: this.fetchError
        });
    },

    fetchSuccess: function (collection, response) {
        console.log('Fetch response: ', response);
    },

    fetchError: function (collection, response) {
        throw new Error("Books fetch error");
    }
});

var PostView = Backbone.View.extend({

    tagName: 'li',

    render: function() {
        this.$el.html(this.model.get('title'));

        return this;
    }

});

var PostsView = Backbone.View.extend({

    render: function() {

        var _this = this;

        this.collection.each(function(post) {

            // Put the current post in the child view
            var _postView = new PostView({ model: post });

            // Render the post and append it to the DOM element of the postsView.
            _this.$el.append(_postView.render().$el);
        });
    }

});

var posts = new Posts();

var postsView = new PostsView({ el: '#js-spa-container', collection: posts });

postsView.render();