phpjs/functions/math/pi.js

php.js offers community built php functions in javascript

function pi() {
  // From: http://phpjs.org/functions
  // +   original by: Onno Marsman
  // +   improved by: dude
  // *     example 1: pi(8723321.4);
  // *     returns 1: 3.141592653589793
  return 3.141592653589793; // Math.PI
}