defaults = function(object, source, guard) {
      var index, iterable = object, result = iterable;
      if (!iterable) return result;
      var args = arguments,
          argsIndex = 0,
          argsLength = typeof guard == 'number' ? 2 : args.length;
      while (++argsIndex < argsLength) {
        iterable = args[argsIndex];
        if (iterable && objectTypes[typeof iterable]) {
        var ownIndex = -1,
            ownProps = objectTypes[typeof iterable] && keys(iterable),
            length = ownProps ? ownProps.length : 0;

        while (++ownIndex < length) {
          index = ownProps[ownIndex];
          if (typeof result[index] == 'undefined') result[index] = iterable[index];
        }
        }
      }
      return result
    }
Assigns own enumerable properties of source object(s) to the destination
object for all destination properties that resolve to `undefined`. Once a
property is set, additional defaults of the same property will be ignored.

@static
@memberOf _
@type Function
@category Objects
@param {Object} object The destination object.
@param {...Object} [source] The source objects.
@param- {Object} [guard] Allows working with `_.reduce` without using its
 `key` and `object` arguments as sources.
@returns {Object} Returns the destination object.
@example

var object = { 'name': 'barney' };
_.defaults(object, { 'name': 'fred', 'employer': 'slate' });
// => { 'name': 'barney', 'employer': 'slate' }