Underscore.js mixin which mimics _.find, except returning the key instead of the value

_.findKey.js

_.mixin({
	findKey: function(obj, predicate, context) {
		var result = null;
		_.some(obj, function(value, index, list) {
			if (predicate.call(context, value, index, list)) {
				result = index;
				return true;
			}
		});
		return result;
	},
});

http://underscorejs.org/#find is the original _.find method