what is the format of timeStamp in onmessage callback?
Hey,

Trying to display timestamp of sent message in basic chat app.

Doing:

```
conn.onmessage = function(e)
{
    console.log(e)
}
```
displays a timeStamp property, however I've no idea of what format it's in.

Doing one message at:

> Thursday 6th September 2018 14:03 returns 123384

and another at:

> Thursday 6th September 2018 14:19 returns 2195683

They're so different (aside from two columns if we prefix the first number with a 0) that I can't tell how they're being generated. They can't be UNIX timestamp as doing a conversion returns 1 Jan 1970... what format is timeStamp in?