phpjs/functions/math/atan2.js

php.js offers community built php functions in javascript

function atan2(y, x) {
  // From: http://phpjs.org/functions
  // +   original by: Brett Zamir (http://brett-zamir.me)
  // *     example 1: atan2(1, 1);
  // *     returns 1: 0.7853981633974483
  return Math.atan2(y, x);
}