Is it possible to use HTML5 local storage to share data between pages from different sites?

Question

I would like to create data on the user side and let javascript from another URL access it too. I am aware of the same origin policy, but I was wondering whether it is possible to create some exceptions. Or, is there any trick/feature I could use?

Answer 1

Best trick I know is to use iframes and postMessage API do get access to localStorage from external domain.

This technique is quite simple:

• on you page you must create iframe to a domain from which you want to get data

• your data domain need listen to message event:

  document.addEventListener ("message", handler, useCapture);

• handler will be responsible for accessing localStorage and posting its content to source domain

• your source domain may call handler function on data domain with postMessage API https://developer.mozilla.org/en-US/docs/DOM/window.postMessage

For security of your data you can use HTTP header X-Frame-Options ALLOW-FROM uri https://developer.mozilla.org/en-US/docs/HTTP/X-Frame-Options?redirectlocale=en-US&redirectslug=The_X-FRAME-OPTIONS_response_header

Hope it will help.