A sample for generating bezier curves

bezier.js

function interpolate(a, b, ratio) {
	return ratio * (b - a) + a;
}

function Point(x, y) { 
  return {x: x, y: y}; 
}

function bezier(points, ratio) {
	if (points.length < 2) return null;

	if (points.length == 2) {
		/*
		 * In the trivial case, we just need to interpolate
		 * between start and end.
		 */
		return Point(
				interpolate(points[0].x, points[1].x, ratio), 
				interpolate(points[0].y, points[1].y, ratio));
	}

	/*
	 * If there are actually control points, then we need to
	 * interpolate between eacn segment formed by those points
	 * (start and end included) and then run bezier on the
	 * points resulting from those interpolations.
	 */
	var interpolated = [];

	for (var i = 1; i < points.length; i++) {
		var prev = points[i - 1];
		var current = points[i];

		interpolated.push(bezier([prev, current], ratio));
	}

	return bezier(interpolated, ratio);
}

var points = [
	Point(0, 150),
	Point(300, 150),
	Point(300, 450),
	Point(600, 450)
];

var canvas = document.getElementById('dpy');
var context = canvas.getContext('2d');

context.beginPath();
context.moveTo(points[0].x, points[0].y);

for (var i = 1; i <= 100; i++) {
	var point = bezier(points, i / 100);
	context.lineTo(point.x, point.y);
}

context.stroke();