assign = 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;
  if (argsLength > 3 && typeof args[argsLength - 2] == 'function') {
    var callback = baseCreateCallback(args[--argsLength - 1], args[argsLength--], 2);
  } else if (argsLength > 2 && typeof args[argsLength - 1] == 'function') {
    callback = args[--argsLength];
  }
  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];
      result[index] = callback ? callback(result[index], iterable[index]) : iterable[index];
    }
    }
  }
  return result
}
Assigns own enumerable properties of source object(s) to the destination
object. Subsequent sources will overwrite property assignments of previous
sources. If a callback is provided it will be executed to produce the
assigned values. The callback is bound to `thisArg` and invoked with two
arguments; (objectValue, sourceValue).

@static
@memberOf _
@type Function
@alias extend
@category Objects
@param {Object} object The destination object.
@param {...Object} [source] The source objects.
@param {Function} [callback] The function to customize assigning values.
@param {*} [thisArg] The `this` binding of `callback`.
@returns {Object} Returns the destination object.
@example

_.assign({ 'name': 'moe' }, { 'age': 40 });
// => { 'name': 'moe', 'age': 40 }

var defaults = _.partialRight(_.assign, function(a, b) {
  return typeof a == 'undefined' ? b : a;
});

var food = { 'name': 'apple' };
defaults(food, { 'name': 'banana', 'type': 'fruit' });
// => { 'name': 'apple', 'type': 'fruit' }