Taken from StackOverflow User Frogz - http://stackoverflow.com/users/405017/phrogz - Originally found here: http://stackoverflow.com/a/4577326/610149

Canvas Dashed Line

var CP = window.CanvasRenderingContext2D && CanvasRenderingContext2D.prototype;
if (CP && CP.lineTo){
	CP.dashedLine = function(x,y,x2,y2,dashArray){
		if (!dashArray) dashArray=[10,5];
		if (dashLength==0) dashLength = 0.001; // Hack for Safari
		var dashCount = dashArray.length;
		this.moveTo(x, y);
		var dx = (x2-x), dy = (y2-y);
		var slope = dy/dx;
		var distRemaining = Math.sqrt( dx*dx + dy*dy );
		var dashIndex=0, draw=true;
		while (distRemaining>=0.1){
			var dashLength = dashArray[dashIndex++%dashCount];
			if (dashLength > distRemaining) dashLength = distRemaining;
			var xStep = Math.sqrt( dashLength*dashLength / (1 + slope*slope) );
			if (dx<0) xStep = -xStep;
			x += xStep
			y += slope*xStep;
			this[draw ? 'lineTo' : 'moveTo'](x,y);
			distRemaining -= dashLength;
			draw = !draw;
		}
	}
}