index.js

const playPauseButton = document.getElementById("play-pause");
let running = false;

const play = () => {
  playPauseButton.textContent = "⏸";
  // calling the step function will trigger consensus, and therefor the render loop
  contract.call(wallet, 'step', BigInt(0), BigInt(1e7), BigInt(0));
  running = true;
};

const pause = () => {
  playPauseButton.textContent = "▶";
  running = false;
};

playPauseButton.addEventListener("click", event => {
  if (running) {
    pause();
  } else {
    play();
  }
});

// replace the old client.pollConsensus call with
client.pollConsensus({
    onRoundEnded: _ => {
        contract.fetchAndPopulateMemoryPages().then(_ => {
            if(running) {
                const results = contract.test(wallet, "render", BigInt(0)).logs[0];
                pre.textContent = results;
                contract.call(wallet, 'step', BigInt(0), BigInt(1e7), BigInt(0));
            }
        });
    }
});

// kick start by calling play()
play()