EventSource is not defined

[edsu]

Works great in Chrome! -- but I see this in Firefox:

ReferenceError: EventSource is not defined

This is a very succinct and powerful example, thanks for sharing it!

[esjewett]

Thank you! Apparently Firefox doesn't support EventSource in web workers. Looks like it's slated to ship in version 53, so if we just wait long enough this issue will resolve itself, which is my preference as this is just a quick demo. https://bugzilla.mozilla.org/show_bug.cgi?id=1267903

If someone wants to send a pull request with a shim or something that is used if EventSource is not defined, that would be welcome!