gistfile1.js

qnet.ModelCollection.prototype.contains = function(obj, identityFn) {
	var objIdentity = identityFn(obj)

	return goog.array.find(this.models, function(model) {
		var modelIdentity = identityFn(model);

		if(modelIdentity == objIdentity) {
			return true;
		} else {
			return false;
		}
	})
}


collection.contains(model, function(m) { return m.getAttribute('GroupID')});

shorter.js

qnet.ModelCollection.prototype.contains = function(obj, identityFn) {
	var objIdentity = identityFn(obj)

	return goog.array.find(this.models, function(model) {
		return objIdentity === identityFn(model);
	})
}