pi.js

// Define a method that rounds pi to a specified decimal place
// Return Pi and how many iterations of the following formula that it took to accomplish
// pi = 4 * (1 – 1/3 + 1/5 – 1/7 + ...)

const calcPi = (scale = 2) => {
  const piTarget = Number(Math.PI).toFixed(scale);

  let piAnswer;
  let accum;
  let denominator = 3;
  let index = 0;

  while (piAnswer !== piTarget) {
    if (index === 0) {
      accum = 1 - (1 / denominator);
    } else {
      let isEven = index % 2;
      denominator += 2;
      if(isEven === 0) {
        accum -= (1 / denominator);
      } else {
        accum += (1 / denominator);
      }
    }
    index++;
    piAnswer = Number(4 * accum).toFixed(scale);
  }

  return [piAnswer, index];
};

const test0 = calcPi(0);
const test1 = calcPi(1);
const test2 = calcPi(2);
const test3 = calcPi(3);
const test4 = calcPi(4);
const test5 = calcPi(5);

console.log(test0);
console.log(test1);
console.log(test2);
console.log(test3);
console.log(test4);
console.log(test5);