​

let approxE = 0;

let iterations = 0;

let div;

let history = [];

​

function setup() {

  createCanvas(600, 400);

  div = createDiv("").style("font-family: sans-serif; font-size: 30px");

}

​

function draw() {

  background(0);

  frameRate(5);

  approxE += 1 / factorial(iterations);

  iterations++;

  history.push(approxE);

  let spacing = width / history.length;

  stroke(255, 0, 0);

  strokeWeight(1);

  noFill();

  let ey = map(Math.E, 1, 3, height, 0);

  line(0, ey, width, ey);

  stroke(255);

  strokeWeight(3);

  beginShape();

  for (let i = 0; i < history.length; i++) {

    const x = i * spacing;

    const y = map(history[i], 1, 3, height, 0);

    vertex(x, y);

  }

  endShape();

  div.html("e ≈ " + approxE);

}

​

function factorial(n) {

  if (n == 0 || n == 1) {

    return 1;

  }

  return n * factorial(n - 1);

}