Javascript Math: get degree between two points

gistfile1.txt

/**
 * return the angle between two points.
 *
 * @param {number} x1		x position of first point
 * @param {number} y1		y position of first point
 * @param {number} x2		x position of second point
 * @param {number} y2		y position of second point
 * @return {number} 		angle between two points (in radian)
 */
Math.getAngle = function( x1, y1, x2, y2 ) {
	
	var	dx = x1 - x2,
		dy = y1 - y2;
	
	return Math.atan2(dy,dx);
};