I looked into using Backbone for my current project, and took a peek at several other MVC libs as well. In the end I decided they all did way more than I was looking for. I just wanted a simple way to separate my models from the DOM. This project seems better than anything else I've seen, but still, 1000 loc seems like a whole lot.

Here's how I'm currently doing it:

    window.models = {}
    function json_to_model(json, parent_model) {
      // Create initial attrs.
      var id = '' + Math.round(Math.random() * 100000000000)
      var children = json.children
      delete json.children
      json['id'] = id;  json.is_expanded = true
      json.child_ids = [];  json.parent_id = null;
      if(parent_model) {
        json.parent_id = parent_model.get('id')
        var child_ids = parent_model.get('child_ids')
        child_ids.push(json.id)
        parent_model.set('child_ids', child_ids)
      }

      // Store models.  Recurse children.
      var new_model = {attrs:json}
      add_get_set(new_model)
      window.models[id] = new_model
      render_model(new_model)
      if(children) {
        for(var i = 0; i < children.length; i++)
          json_to_model(children[i], new_model)
      }
      return new_model
    }

    // Get and set.  Render on set.
    function add_get_set(model) {
      model.get = function(key){ return this.attrs[key] }
      model.set = function(key, val) {
        this.attrs[key] = val
        render_model(this)
        localStorage.setItem('models', JSON.stringify(window.models))
      }
    }

Now, that doesn't do much. But for prototyping a gui, it seems pretty good. Less is more. I wonder how little code I can add to get it to work with a real backend.