JSFiddle - React, Tailwind, and code Playground

JavaScript

const iterations = 10000000;
const size = 500;

let inside = 0;
for (let i = 0; i < iterations; i++) {
  var Xpos = Math.random() * size;
  var Ypos = Math.random() * size;

  var dist = Math.hypot(Xpos - size / 2, Ypos - size / 2);

  if (dist < size / 2) {
    inside++;
  }
}

alert((4 * inside) / iterations);