lodash/_copyObject.js

define(['./_assignValue', './_baseAssignValue'], function(assignValue, baseAssignValue) {

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

  /**
   * Copies properties of `source` to `object`.
   *
   * @private
   * @param {Object} source The object to copy properties from.
   * @param {Array} props The property identifiers to copy.
   * @param {Object} [object={}] The object to copy properties to.
   * @param {Function} [customizer] The function to customize copied values.
   * @returns {Object} Returns `object`.
   */
  function copyObject(source, props, object, customizer) {
    var isNew = !object;
    object || (object = {});

    var index = -1,
        length = props.length;

    while (++index < length) {
      var key = props[index];

      var newValue = customizer
        ? customizer(object[key], source[key], key, object, source)
        : undefined;

      if (newValue === undefined) {
        newValue = source[key];
      }
      if (isNew) {
        baseAssignValue(object, key, newValue);
      } else {
        assignValue(object, key, newValue);
      }
    }
    return object;
  }

  return copyObject;
});