lodash/internal/createDefaults.js

define(['../function/restParam'], function(restParam) {

  /** Used as a safe reference for `undefined` in pre-ES5 environments. */
  var undefined;

  /**
   * Creates a `_.defaults` or `_.defaultsDeep` function.
   *
   * @private
   * @param {Function} assigner The function to assign values.
   * @param {Function} customizer The function to customize assigned values.
   * @returns {Function} Returns the new defaults function.
   */
  function createDefaults(assigner, customizer) {
    return restParam(function(args) {
      var object = args[0];
      if (object == null) {
        return object;
      }
      args.push(customizer);
      return assigner.apply(undefined, args);
    });
  }

  return createDefaults;
});