communicate with html iframe child window

how to easily interact communication between html parent window and child iframe window ?
use html5 localStorage if both parent and child window are in the same folder.
you can find a javascript example in my osm car sim json_osm_webcarsimheight_shadow and mystreetview

=>  http://chungswebsite.blogspot.fr/search/label/json_osm_chung     (free open source)