Should not abort connections on beforeunload event

[SQReder]

You want to:

• report a bug
• request a feature

Current behaviour

Polling transport breaks every time after beforeunload triggered, even if page wasn't closed after event have have has handed.

Setup

• browser: Chrome
• engine.io version: 1.1.0+

Other information

It should be replaced at least to unload or better pagehide event (which one is good supported - 93%)

We have had got very annoying floating bug with socket.io long-polling, which was stable reproduced with selenium tests in Chrome on Linux host, and all works well on windows host. Sometimes Chrome with no obvious reason want to freeze page, and so beforeunload triggered, so app is broken after that.

Here some related info:
Page lifecycle api:

• Legacy API to avoid
• Page lifecycle diagram

PageTransitionEvent browsers support

[SQReder]

Related to #406

[darrachequesne]

I guess we could add something like:

if ('onpagehide' in window) {
   addEventListener('pagehide', unloadHandler, false);
} else {
   addEventListener('beforeunload', unloadHandler, false);
}

So as not to break 7% of the users. WDYT?

[SQReder]

How about this one? It use pagehide when available, will correctly terminate connections on unload, and also not break things when beforeunload was cancelled.

var terminationEvent = 'onpagehide' in window ? 'pagehide' : 'unload';
addEventListener(terminationEvent, unloadHandler, false);