copy from this site. http://lab.polygonal.de/articles/recursive-dimensional-clustering/

RDC.js

var Entity = function (type, pos, obj) {
	this.type = type;
	this.pos = pos;
	this.obj = obj;
}

var RDC = function (collide) {
	this.collide = collide;
}
RDC.SUBDIVISION_THRESHOLD = 4;
RDC.CONTACT_THRESHOLD = 0.001;

RDC.prototype.bruteForce = function (group) {
	for (var i=0,l=group.length; i<l; i++) {
		for (var j=i+1; j<k; j++) {
			this.collide(group[i], group[j]);
		}
	}
};
RDC.prototype.recursiveClustering = function (group, axis1, axis2) {
	if (axis1 === -1 || group.length < RDC.SUBDIVISION_THRESHOLD) {
		this.bruteForce(group);
	} else {
		var boundaries = this.getOpenCloseBounds(group, axis1);		
		boundaries.sort(function (a, b) {
			return a.pos - b.pos;
		});
		
		var newAxis1 = axis2,
			newAxis2 = -1,
			groupSubdivided = false,
			subgroup = [],
			count = 0,
			l = boundaries.length;
		for (var i=0; i<l; i++)
		{
			var b = boundaries[i];
			if (b.type == "open") {
				count++;
				subgroup.push(b.obj);
			} else {
				count--;
				if (count == 0) {
					if (i != (k - 1)) {
						groupSubdivided = true;
					}
					
					if (groupSubdivided) {
						if (axis1 == 0) {
							newAxis1 = 1;
						} else if (axis1 == 1) {
							newAxis1 = 0;
						}
					}
					
					this.recursiveClustering(subgroup, newAxis1, newAxis2);
					subgroup = [];
				}
			}
		}
	}
};
RDC.prototype.getOpenCloseBounds = function (group, axis) {
	var l = group.length,
		boundaries = [];
	
	switch(axis)
	{
		case 0:
			for (i=0; i<l; i++) {
				o = group[i];
				boundaries.push(new Entity("open",  o.x - o.radius + RDC.CONTACT_THRESHOLD, o));
				boundaries.push(new Entity("close", o.x + o.radius - RDC.CONTACT_THRESHOLD, o));
			}
			break;
		case 1:
			for (i=0; i<l; i++) {
				o = group[i];
				boundaries.push(new Entity("open",  o.y - o.radius + RDC.CONTACT_THRESHOLD, o));
				boundaries.push(new Entity("close", o.y + o.radius - RDC.CONTACT_THRESHOLD, o));
			}
	}
	return boundaries;
}