JavaScript Date Object - Handy Extensions

I like to extend the JavaScript Date object a little bit, to provide me with the one true date format, aka: ISO8601.

Date.prototype.toISO8601()
{
	var r = this.getFullYear()
		+ '-' + ('0' + (this.getMonth() + 1)).substr(-2)
		+ '-' + ('0' + this.getDate()).substr(-2)
		+ 'T' + ('0' + this.getHours()).substr(-2)
		+ ':' + ('0' + this.getMinutes()).substr(-2)
		+ ':' + ('0' + this.getSeconds()).substr(-2)
	// Timezone shit
	// var tz = 
}

Date.prototype.toISO8601UTC()
{
	var r = this.getUTCFullYear()
		+ '-' + ('0' + (this.getUTCMonth() + 1)).substr(-2)
		+ '-' + ('0' + this.getUTCDate()).substr(-2)
		+ 'T' + ('0' + this.getUTCHours()).substr(-2)
		+ ':' + ('0' + this.getUTCMinutes()).substr(-2)
		+ ':' + ('0' + this.getUTCSeconds()).substr(-2)
		+ 'Z';
	return r;
}