index.html

<html>
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/0.8.0/p5.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/0.8.0/addons/p5.dom.js"></script>
<script src=https://cdnjs.cloudflare.com/ajax/libs/mathjs/3.3.0/math.min.js></script>
<script>

let xspacing = 16; // Distance between each horizontal location
let w; // Width of entire wave
let theta = 0.0; // Start angle at 0
let amplitude = 75.0; // Height of wave
let period = 500.0; // How many pixels before the wave repeats
let dx; // Value for incrementing x
let yvalues; // Using an array to store height values for the wave
let f_x = 'sin(x)';

function processInput(){
  const name = input.value();
  f_x = name;
}

function setup() {
  createCanvas(710, 400);
  w = width + 16;
  dx = (TWO_PI / period) * xspacing;
  yvalues = new Array(floor(w / xspacing));
  input = createInput();
  input.position(20, 65);

  button = createButton('Use');
  button.position(input.x + input.width, 65);
  button.mousePressed(processInput);

  greeting = createElement('h2', 'Animated Plotter');
  greeting.position(20, 5);

  textAlign(CENTER);
  textSize(50);

}

function draw() {
  background(0);
  calcWave();
  renderWave();
}

function calcWave() {
  // Increment theta (try different values for
  // 'angular velocity' here)
  theta += 0.02;

  // For every x value, calculate a y value with sine function
  let x = theta;
  for (let i = 0; i < yvalues.length; i++) {
    yvalues[i] = eval(f_x) * amplitude;
    x += dx;
  }
}

function renderWave() {
  noStroke();
  fill(255);
  // A simple way to draw the wave with an ellipse at each location
  for (let x = 0; x < yvalues.length; x++) {
    ellipse(x * xspacing, height / 2 + yvalues[x], 16, 16);
  }
}
</script>
</html>