HTML and CSS Reference
Now you need to add code to initiate the messaging.
Channel messaging works by creating a pair of ports. A port is a generic object that allows
messaging. It supports the postMessage method and onmessage event that you're fa-
miliar with from cross-document messaging. Anything sent to one port will appear as out-
put from the other port; in HTML5 terms they're described as entangled . This is by ana-
logy to quantum entanglement : two particles that, no matter what distance separates them,
change simultaneously. One of the ports is then sent to another script context. This could be
a script in another document or window or a web worker. ListingF.2 shows the details. The
code from listing F.2 should go in a <script> block after the form in example-1.html
(you could add it in the head element, but then you'd need to wrap it in a function and
execute it on the load event). As you can see, the channel-messaging API is similar to the
cross-document messaging API you looked at in chapter 4 .