Can HTML5 local storage be used to exchange data between pages from different sites?

Question

I would like to create data on the user side and allow javascript from another URL to access it. I know about the same origin policy, but I was wondering if some exceptions could be created. Or is there a trick / feature that I could use?

Answer 1

The best trick I know is to use iframes and the postMessage API to access localStorage from an external domain.

This technique is pretty simple:

• on your page, you must create an iframe for the domain from which you want to receive data.

• Your data domain needs to listen to the message event:

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

• the handler will be responsible for accessing localStorage and sending its contents to the source domain

• your source domain can call the handler function in the data area using the postMessage API https://developer.mozilla.org/en-US/docs/DOM/window.postMessage

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

Hope this helps.