Awesome
immutable-quadtree-js
Immutable Quadtree in JS
Example
var a = new ImmutableQuadTree(4);
var b = a.add('0000', {_id: 'ABC'});
var c = b.add('0000', {_id: 'ABC'});
var d = c.add('0010', {_id: 'BBB'});
a === b; // false
b === c; // true
c === d; // false
var e = d.keep('001');