How can I dynamically set a className for a Backbone.js view based on it's model attributes?

Question

Basically what I need is to do something like this

App.CommentView = Backbone.View.extend({
  className: function() {
    if (this.model.get('parent_id')) {
      return 'comment comment-reply';
    } else {
     return 'comment';
    }
  },

The problem is, that at the function passed to className is executed in context of the html of the view template, so I can't call this.model.

Is there any way I can access the model at this point in the rendering process? Or do I need to set the class later, for example in the render function?

Answer 1

This sounds like a job for model binding.

App.CommentView = Backbone.View.extend({
  initialize: function () {
      // anytime the model's name attribute changes
      this.listenTo(this.model, 'change:name', function (name) {
          if (name === 'hi') {
             this.$el.addClass('hi');
          } else if......
      });
  },
  render: function () {
       // do initial dynamic class set here
  }

Answer 2

You should use the attributes hash/function:

attributes: function () {
 //GET CLASS NAME FROM MODEL
 return { 'class' : this.getClass() }
},
getClass: function() {
   return this.model.get('classname')
}

Answer 3

It would be much easier I think to use this.$el.toggleClass or simply add the class inside render.

However if you want to set the class when constructing the view, you can pass it as an option:

view = new App.CommentView({
  model: model,
  className: model.get('parent_id') ? 'comment comment-reply' : 'comment'
})

Answer 4

I did it at View initialize

App.CommentView = Backbone.View.extend({
    initialize: function() {
        if(this.model.get("parent_id"))
            this.$el.addClass("comment-reply");
    },