const square = document.querySelector('.raf');

const jank = document.querySelector('input');

let last = 0;

requestAnimationFrame(function f(ts) {

  if(jank.checked) {

    // noprotect

    for(var i = 0; i<1e8; i++);

  }

  requestAnimationFrame(f);

  if (last === 0)

    return (last = ts);

​

  const delta = ts - last;

  last = ts;

  square.style.transform = `rotate(${ts/1000}turn)`;

});

​

​