A pairing function (szudzik) that supports negative numbers

szudzik.js

// src https://codepen.io/sachmata/post/elegant-pairing

szudzik.getindex = function(x, y) {
    var xx = x >= 0 ? x * 2 : x * -2 - 1;
    var yy = y >= 0 ? y * 2 : y * -2 - 1;
    return (xx >= yy) ? (xx * xx + xx + yy) : (yy * yy + xx);
};

szudzik.unpair = function(z) {
    var sqrtz = Math.floor(Math.sqrt(z));
    var sqz = sqrtz * sqrtz;
    var result1 = ((z - sqz) >= sqrtz) ? [sqrtz, z - sqz - sqrtz] : [z - sqz, sqrtz];
    var xx = result1[0] % 2 === 0 ? result1[0] / 2 : (result1[0] + 1) / -2;
    var yy = result1[1] % 2 === 0 ? result1[1] / 2 : (result1[1] + 1) / -2;
    return [xx, yy];
};

Thanks nick and TheGreatRambler!