xyzToBounds.js

var EXTENT = [-Math.PI * 6378137, Math.PI * 6378137];

function xyzToBounds(x, y, z) {
    var tileSize = EXTENT[1] * 2 / Math.pow(2, z);
    var minx = EXTENT[0] + x * tileSize;
    var maxx = EXTENT[0] + (x + 1) * tileSize;
    // remember y origin starts at top
    var miny = EXTENT[1] - (y + 1) * tileSize;
    var maxy = EXTENT[1] - y * tileSize;
    return [minx, miny, maxx, maxy];
}