BackboneJS Rendering Problems

Question

For the last six months I've been working with Backbone. The first two months were messing around, learning and figuring out how I want to structure my code around it. The next 4 months were pounding away a production-fit application. Don't get me wrong, Backbone has saved me from the thousands-lines mess of client side code that were the standard before, but it enabled me to do more grandiose things in less time, opening up a complete new stack of problems. For all the questions I raise here there are simple solutions that feels like hacks or just feel wrong. I promise a 300 points bounty for an awesome solution. Here goes:

1. Loading - For our use case (an admin panel) pessimistic syncing is bad. For some things I need to validate things on the server before accepting them. We started out before the 'sync' event was merged into Backbone,

and we used this little code for mimicking the loading event:

window.old_sync = Backbone.sync  # Add a loading event to backbone.sync Backbone.sync = (method, model, options) ->   old_sync(method, model, options)   model.trigger("loading") 

Great. It works as expected but it doesn't feel correct. We bind this event to all the relevant views and display a loading icon until we receive a success or error event from that model. Is there a better, saner, way to do this?

Now for the hard ones:

2. Too many things render themselves too much - Let's say our application have tabs. Every tab controls a collection. On the left side you get the collection. You click a model to start editing it at the center. You change its name and press tab to get to the next form item. Now, your app is a "real time something something" that notices the difference, runs validations, and automatically sync the change to the server, no save button required! Great, but the H2 at the start of the form is the same name as in the input - you need to update it. Oh, and you need to update the name on the list to the side. OH, and the list sorts itself by names!

Here's another example: You want to create a new item in the collection. You press the "new" button and you start filling out the form. Do you immediately add the item to the collection? But what happens if you decided to discard it? Or if you save the entire collection on another tab? And, there's a file upload - You need to save and sync the model before you can start uploading the file (so you can attach the file to the model). So everything starts rendering in tremors: You save the model and the list and the form renders themselves again - it's synced now, so you get a new delete button, and it shows in the list - but now the file upload finished uploading, so everything starts rendering again.

Add subviews to the mix and everything starts looking like a Fellini movie.

3. It's subviews all the way down - Here's a good article about this stuff. I could not, for the love of everything that is holy, find a correct way to attach jQuery plugins or DOM events to any view that has subviews. Hell ensues promptly. Tooltips hear a render coming a long and start freaking around, subviews become zombie-like or do not respond. This is the main pain points as here actual bugs stand, but I still don't have an all encompassing solution.

4. Flickering - Rendering is fast. In fact, it is so fast that my screen looks like it had a seizure. Sometimes it's images that has to load again (with another server call!), so the html minimizes and then maximizes again abruptly - a css width+height for that element will fix that. sometimes we can solve this with a fadeIn and a fadeOut - which are a pain in the ass to write, since sometimes we're reusing a view and sometimes creating it anew.

TL;DR - I'm having problems with views and subviews in Backbone - It renders too many times, it flickers when it renders, subviews detach my DOM events and eat my brains.

Thank you!

More details: BackboneJS with the Ruby on Rails Gem. Templates using UnderscoreJS templates.

Answer 1

Partial rendering of views

In order to minimize the full rendering of your DOM hierarchy, you can set up special nodes in your DOM that will reflect updates on a given property.

Let's use this simple Underscore template, a list of names:

<ul>   <% _(children).each(function(model) { %>     <li>         <span class='model-<%= model.cid %>-name'><%= model.name %></span> :         <span class='model-<%= model.cid %>-name'><%= model.name %></span>     </li>   <% }); %> </ul> 

Notice the class model-<%= model.cid %>-name, this will be our point of injection.

We can then define a base view (or modify Backbone.View) to fill these nodes with the appropriate values when they are updated:

var V = Backbone.View.extend({     initialize: function () {         // bind all changes to the models in the collection         this.collection.on('change', this.autoupdate, this);     },      // grab the changes and fill any zone set to receive the values     autoupdate: function (model) {         var _this = this,             changes = model.changedAttributes(),             attrs = _.keys(changes);          _.each(attrs, function (attr) {             _this.$('.model-' + model.cid + '-' + attr).html(model.get(attr));         });     },      // render the complete template     // should only happen when there really is a dramatic change to the view     render: function () {         var data, html;          // build the data to render the template         // this.collection.toJSON() with the cid added, in fact         data = this.collection.map(function (model) {             return _.extend(model.toJSON(), {cid: model.cid});         });          html = template({children: data});         this.$el.html(html);          return this;     } }); 

The code would vary a bit to accommodate a model instead of a collection. A Fiddle to play with http://jsfiddle.net/nikoshr/cfcDX/

Limiting the DOM manipulations

Delegating the rendering to the subviews can be costly, their HTML fragments have to be inserted into the DOM of the parent. Have a look at this jsperf test comparing different methods of rendering

The gist of it is that generating the complete HTML structure and then applying views is much faster than building views and subviews and then cascading the rendering. For example,

<script id="tpl-table" type="text/template">     <table>         <thead>             <tr>                 <th>Row</th>                 <th>Name</th>             </tr>         </thead>         <tbody>         <% _(children).each(function(model) { %>             <tr id='<%= model.cid %>'>                 <td><%= model.row %></td>                 <td><%= model.name %></td>             </tr>         <% }); %>         </tbody>      </table> </script> 

var ItemView = Backbone.View.extend({ });  var ListView = Backbone.View.extend({     render: function () {         var data, html, $table, template = this.options.template;          data = this.collection.map(function (model) {             return _.extend(model.toJSON(), {                 cid: model.cid             });         });          html = this.options.template({             children: data         });          $table = $(html);          this.collection.each(function (model) {             var subview = new ItemView({                 el: $table.find("#" + model.cid),                 model: model             });         });          this.$el.empty();         this.$el.append($table);          return this;     } });   var view = new ListView({     template: _.template($('#tpl-table').html()),     collection: new Backbone.Collection(data) }); 

http://jsfiddle.net/nikoshr/UeefE/

Note that the jsperf shows that the template can be be split into subtemplates without too much penalty, which would allow you to provide a partial rendering for the rows.

On a related note, don't work on nodes attached to the DOM, this will cause unnecessary reflows. Either create a new DOM or detach the node before manipulating it.

Squashing zombies

Derick Bailey wrote an excellent article on the subject of eradicating zombie views

Basically, you have to remember that when you discard a view, you must unbind all listeners and perform any additional cleanup like destroying the jQuery plugin instances. What I use is a combination of methods similar to what Derick uses in Backbone.Marionette:

var BaseView = Backbone.View.extend({      initialize: function () {         // list of subviews         this.views = [];     },      // handle the subviews     // override to destroy jQuery plugin instances     unstage: function () {         if (!this.views) {             return;         }          var i, l = this.views.length;          for (i = 0; i < l; i = i + 1) {             this.views[i].destroy();         }         this.views = [];     },      // override to setup jQuery plugin instances     stage: function () {     },      // destroy the view     destroy: function () {         this.unstage();         this.remove();         this.off();          if (this.collection) {             this.collection.off(null, null, this);         }         if (this.model) {             this.model.off(null, null, this);         }     } }); 

Updating my previous example to give the rows a draggable behavior would look like this:

var ItemView = BaseView.extend({     stage: function () {         this.$el.draggable({             revert: "invalid",             helper: "clone"         });     },      unstage: function () {         this.$el.draggable('destroy');         BaseView.prototype.unstage.call(this);     } });  var ListView = BaseView.extend({      render: function () {        //same as before          this.unstage();         this.collection.each(function (model) {             var subview = new ItemView({                 el: $table.find("#" + model.cid),                 model: model             });             subview.stage();             this.views.push(subview);         }, this);         this.stage();          this.$el.empty();         this.$el.append($table);          return this;     } }); 

http://jsfiddle.net/nikoshr/yL7g6/

Destroying the root view will traverse the hierarchy of views and perform the necessary cleanups.

NB: sorry about the JS code, I'm not familiar enough with Coffeescript to provide accurate snippets.

Answer 2

Ok, in order.. :)

1. Loading...

In case you want to validate data which stored on server, good practice do it on server-side. If validation on server will be unsuccessful, server should send not 200 HTTP code, therefore save metod of Backbone.Model will trigger error.

Other side, for validation data backbone has unimplemented validate method. I guess that right choise to implement and use it. But keep in mind that validate is called before set and save, and if validate returns an error, set and save will not continue, and the model attributes will not be modified. Failed validations trigger an "error" event.

Another way, when we call silent set(with {silent: true} param), we should call isValid method manually to validate data.

2. Too many things render themselves too much..

You have to separate your Views under their logic. Good practice for collection is separate view for each model. In this case you could render each element independently. And even more - when you initalizing your container view for collection, you could bind any event from each model in the collection to appropriate view, and they will render automatically.

Great, but the H2 at the start of the form is the same name as in the input - you need to update it. Oh, and you need to update the name on the list to the side.

you could use JQuery on method to implement callback which send value to display. Example:

//Container view init: function() {     this.collection = new Backbone.Collection({         url: 'http://mybestpage.com/collection'     });     this.collection.bind('change', this.render, this);     this.collection.fetch(); }, render: function() {      _.each(this.collection.models, function(model) {          var newView = new myItemView({               model: model,               name: 'view' + model.id          });          this.$('#my-collection').append(newView.render().$el);          view.on('viewEdit', this.displayValue);     }, this); }, ... displayValue: function(value) {     //method 1     this.displayView.setText(value); //we can create little inner view before,                                       //for text displaying. Сonvenient at times.     this.displayView.render();     //method 2     $(this.el).find('#display').html(value); }  //View from collection myItemView = Backbone.View.extend({ events: {     'click #edit': 'edit' }, init: function(options) {     this.name = options.name; }, ... edit: function() {     this.trigger('viewEdit', this.name, this); } 

OH, and the list sorts itself by names!

You can use sort method for backbone collections. But (!) Calling sort triggers the collection's "reset" event. Pass {silent: true} to avoid this. How to

Here's another example: You want to create a new item in the collection...

When we press a "New" button we need to create a new model, but only when .save() method will trigger success, we should push this model to collection. In another case we should display error message. Of course we have no reasons to add a new model to our collection until it has been validated and saved on server.

3. It's subviews all the way down... subviews become zombie-like or do not respond.

when you (or any model) calling render method, all elements inside it will be recreated. So in case when you have subviews, you should call subView.delegateEvents(subView.events); for all of subviews; Probably this method is little trick, but it works.

4. Flickering..

Using thumbnails for big and medium images will minimize flickering in lot of cases. Other way, you could separate rendering of view to images and other content.

Example:

var smartView = Backbone.View.extend({   initialize: function(){     this.model.on( "imageUpdate", this.imageUpdate, this );     this.model.on( "contentUpdate", this.contentUpdate, this );   },    render: function(){     this.$el.html(this.template(this.model.toJSON()));   },    imageUpdate: function(){     this.$el.find('#image').attr('src', this.model.get('imageUrl'));   },   contentUpdate: function(){     this.$el.find('#content').html(this.model.get('content'));   } }) 

I hope this helps anyone. Sorry for grammar mistakes, if any :)