How do I get a UTC Timestamp in JavaScript?

While writing a web application, it makes sense to store (server side) all datetimes in the DB as UTC timestamps.

I was astonished when I noticed that you couldn’t natively do much in terms of Timezone manipulation in JavaScript.

I extended the Date object a little. Does this function make sense? Basically, every time I send anything to the server, it’s going to be a timestamp formatted with this function…

Can you see any major problems here? Or maybe a solution from a different angle?

Date.prototype.getUTCTime = function(){ 
  return new Date(
    this.getUTCFullYear(),
    this.getUTCMonth(),
    this.getUTCDate(),
    this.getUTCHours(),
    this.getUTCMinutes(), 
    this.getUTCSeconds()
  ).getTime(); 
}

It just seems a little convoluted to me. And I am not so sure about performance either.