Convert LAMBERT93 coordinates to WGS with JS

lambert-converter.js

// this function converts LAMBERT93 coordinates used by IGN to lat / lon coordinates
// found here https://gist.github.com/will83/5920606
const toWGS = (x, y) => {
  const b7 = 298.257222101;
  const b8 = 1 / b7;
  const b9 = 2 * b8 - b8 * b8;
  const b10 = Math.sqrt(b9);
  const b13 = 3;
  const b14 = 700000;
  const b15 = 12655612.0499;
  const b16 = 0.725607765053267;
  const b17 = 11754255.426096;
  const delx = x - b14;
  const dely = y - b15;
  const gamma = Math.atan(-delx / dely);
  const r = Math.sqrt(delx * delx + dely * dely);
  const latiso = Math.log(b17 / r) / b16;
  const sinphiit0 = Math.tanh(latiso + b10 * Math.atanh(b10 * Math.sin(1)));
  const sinphiit1 = Math.tanh(latiso + b10 * Math.atanh(b10 * sinphiit0));
  const sinphiit2 = Math.tanh(latiso + b10 * Math.atanh(b10 * sinphiit1));
  const sinphiit3 = Math.tanh(latiso + b10 * Math.atanh(b10 * sinphiit2));
  const sinphiit4 = Math.tanh(latiso + b10 * Math.atanh(b10 * sinphiit3));
  const sinphiit5 = Math.tanh(latiso + b10 * Math.atanh(b10 * sinphiit4));
  const sinphiit6 = Math.tanh(latiso + b10 * Math.atanh(b10 * sinphiit5));
  const longrad = gamma / b16 + b13 / 180 * Math.PI;
  const latrad = Math.asin(sinphiit6);
  const lng = longrad / Math.PI * 180;
  const lat = latrad / Math.PI * 180;

  return [lat, lng];
};

export default toWGS;