js计算点到原点的距离

<script type="text/javascript">
	function Point(x,y){
		this.x = x;
		this.y = y;
	}
	
	var p = new Point(1,1);
	
	Point.prototype.r = function(){
		return Math.sqrt(
			this.x*this.x+this.y*this.y		
		);
	};
	
	alert(p.r());
</script>