1  var eq = require('./eq');
 2  
 3  /** Used for built-in method references. */
 4  var objectProto = Object.prototype;
 5  
 6  /** Used to check objects for own properties. */
 7  var hasOwnProperty = objectProto.hasOwnProperty;
 8  
 9  /**
10   * Used by `_.defaults` to customize its `_.assignIn` use to assign properties
11   * of source objects to the destination object for all destination properties
12   * that resolve to `undefined`.
13   *
14   * @private
15   * @param {*} objValue The destination value.
16   * @param {*} srcValue The source value.
17   * @param {string} key The key of the property to assign.
18   * @param {Object} object The parent object of `objValue`.
19   * @returns {*} Returns the value to assign.
20   */
21  function customDefaultsAssignIn(objValue, srcValue, key, object) {
22    if (objValue === undefined ||
23        (eq(objValue, objectProto[key]) && !hasOwnProperty.call(object, key))) {
24      return srcValue;
25    }
26    return objValue;
27  }
28  
29  module.exports = customDefaultsAssignIn;