Question

As mentioned in @andorov’s answer, the OP’s ideal code (<div style="width:{{model.width}}"> now pretty much just works as of Ember 1.10

I am new to Ember.js, and I am finding it difficult to dynamically
change CSS. Here is an example to explain what I mean:

var App = Em.Application.create();

App.MyObj=Em.Object.extend({
    objWidth:10
});

App.objController = Ember.ArrayController.create({
    content: [],
  createObj: function(){
      var obj = App.MyObj.create();
      this.pushObject(obj);
  }
});

The code below doesn’t work, but it explains my goal. Using a
Handlebars template, I want to accomplish this:

{{#each obj in App.objController}}
     <div style="width:{{obj.objWidth}}"></div>
{{/each}}

In other words, I just want to have the width of the <div> update
when the objWidth property is changed.

Answer 1

The style property has to be bound with bindAttr, passing the style as a whole, not just one of the properties, as it doesn’t understand that. This property only gives you access to the style as a string, targeting the immediate element. It’s not possible to bind to a property of the style if you define it like that.

So here’s my sugestion: I’ve created a couple of “model” classes like the following, implementing a property that returns the width in pixels:

var WidthEnabledModel = Em.Object.extend({
    width: 100,
    unit: "px",
    widthString: function() {
        return 'width: %@%@'.fmt(this.width, this.unit);
    }.property('width', 'unit')            
});

App.SampleModel = WidthEnabledModel.extend({
    itemName: ''
});

Then, for each item in your collection I’m binding that property to the style attribute:

<script type="text/x-handlebars" data-template-name="sample">
    <div id="sample_area" style="width: 250px;">
    {{#each thing in controller.content}}
      <div class="item" {{bindAttr style="thing.widthString"}}>
          {{thing.itemName}}<br />
          {{thing.widthString}}
      </div>
    {{/each}}
    <div>
</script>

Follow the example with full code I’ve made at jsfiddle here http://jsfiddle.net/schawaska/ftWZ6/

Edit:
I’ve made some changes in the fiddle to add more feature, but the part to set the width stays the same.