In the unlikely case that, instead of returning JSON from the server as you should, you do end up parsing this yourself, here's how you might do that:
initializer
  .replace(/^\{|\}$/g, '')            // remove {} at beginning and end
  .split(',')                         // break apart into key: val pairs
  .reduce(function(result, keyval) {  // build object 
    var parts = keyval.split(':').map(''.trim);
    result[parts[0]] = parts[1];
    return result;
  }, {});
Of course, you'd probably want to add a bunch of bullet-proofing to that.
If you're using Underscore, you could use its ability to create an object from an array of [key, val] pairs:
_.object(initializer
  .replace((/^\{|\}$/g, '')
  .split(',')
  .map(function(keyval) {
    return keyval.split(':').map(''.trim);
  })
);