postMessage() API for <embed-page/> demo, Embeddable Progressive Applications Working Group

<embed-page/> mimicks the window object in context of postMessage() API. See postMessage for details.

epa 0

epa 1

postMessage events log
message event contentorigin url
Manual test
postMessage-app.html listens to "message" event and appends data to log matrix.
It is served within IFRAME and two embed-page instances.

The common load sequence is
1. postMessage-app.js listens for "message" event.
2. postMessage-app.js will send to opener message with own URL.
3. "message" event handler appends data to log table

IFRAME
    1-3. as in common part.
    4. ?from=iframe added to page log matrix
    5.  to post to IFRAME, observe appearance of ?from=demo inside of IFRAME log matrix

embed-page - main
    1-3. as in common part.
    4. observe ?from=epa0 in page log matrix
    5.  to post to epa, observe appearance of ?from=demo within epa log matrix

embed-page - second
    1-4. as in embed-page - main part.
    5.  to post to epa, observe appearance of ?from=demo within epa log matrix

postMessage-app.js When used from embed-page, behaves same way as from IFRAME.
Demo IFRAME postMessage-app.html