YourJS candidate function: swapProps()

swapProps.js

/**
 * Swaps the specified properties between the target object and the source object.
 * @param {*} target
 *   Target object from which the specified properties will be swapped. 
 * @param {*} source
 *   Source object from which the specified properties will be swapped.
 * @param {Array<number|string>} keys
 *   Array of keys for the properties that should be swapped between source and
 *   target.
 * @param {boolean=} [opt_dontDelete=false]
 *   Indicates whether properties that dont exist should be deleted between objects.
 *   If `true`, non-existent properties will be set to `undefined`.
 * @returns {*}
 *   Returns a reference to `target`.
 */
function swapProps(target, source, props, opt_dontDelete) {
  source = Object(source);
  for (var t, copyToSource, prop, oTarget = Object(target), i = props.length; i--;) {
    prop = props[i];
    copyToSource = prop in oTarget;
    t = oTarget[prop];
    if ((prop in source) || opt_dontDelete) {
      oTarget[prop] = source[prop];
    }
    else {
      delete oTarget[prop];
    }
    if (copyToSource || opt_dontDelete) {
      source[prop] = t;
    }
    else {
      delete source[prop];
    }
  }
  return target;
}