computePi.js

function computePi() {
  document.getElementById('pi').innerHTML = (4 * atan(1/5) - atan(1/239)) * 4
}

function atan(x) {
  var result = x;
  var xSquared = x * x;
  
  var term = x;
  var divisor = 1;
  
  while (term != 0) {
    divisor += 2;
    term *= xSquared;
    result -= term / divisor;

    divisor += 2;
    term *= xSquared;
    result += term / divisor;
  }
  
  return result;
}