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 + ...)

function* pi() {
  let n = 1;
  let series = 0;

  while(true) {
    next = 1/(n*2-1)

    if (n % 2 == 0) {
      next = -next
    }

    series += next

    yield [4*series, n++]
  }
}

const roundPi = (scale) => {
  const target = Math.PI.toFixed(scale)
  const piGenerator = pi()

  for(const [value, iteration] of piGenerator) {
    const rounded = value.toFixed(scale)
    if (rounded === target) {
      return [rounded, iteration]
    }
  }
}

for (let i = 1; i <= 5; i++) {
  const [value, iterations] = roundPi(i)
  console.log(`Value: ${value} / Iterations: ${iterations}`)
}