phpjs/functions/math/atanh.js

php.js offers community built php functions in javascript

function atanh(arg) {
  //  discuss at: http://phpjs.org/functions/atanh/
  // original by: Onno Marsman
  //   example 1: atanh(0.3);
  //   returns 1: 0.3095196042031118

  return 0.5 * Math.log((1 + arg) / (1 - arg));
}