code: function insertDependentKey( map, key, currentIndex, arr ) {
  	const weakMapKey = key || STATIC_FALSY_KEY;
  
  	const existingMap = map.get( weakMapKey );
  	if ( existingMap ) {
  		return existingMap;
  	}
  
  	const newMap = currentIndex === arr.length - 1 ? new Map() : new WeakMap();
  	map.set( weakMapKey, newMap );
  	return newMap;
  }
docs: /*
  First tries to get the value for the key.
  If the key is not present, then inserts a new map and returns it
  
  Note: Inserts WeakMaps except for the last map which will be a regular Map.
  The last map is a regular one because the the key for the last map is the string results of args.join().