Edit in JSFiddle

const startTest = () => {
	const isPrime = (candidate) => {
  	for (let i = 2; i <= Math.floor(Math.sqrt(candidate)); i++) {
    	if (candidate % i === 0) return false;
    }
    return true;
  }

	let buffer = new ArrayBuffer(1024 * 1024 * 2)
  let view = new Uint8Array(buffer);
  
  let count = 0;
  performance.mark('startTest');
  for (let i = 0; i < view.length; i++) {
  	let candidate = i + 2;
    let result = isPrime(candidate);
    if (result) count++
    view[i] = result;
  }
  performance.mark('endTest');
  performance.measure('primes', 'startTest', 'endTest');
  document.getElementById('performance').innerHTML = `Found ${count} in ${performance.getEntriesByName('primes')[0].duration} ms`;
}
document.getElementById('test').addEventListener('click', startTest);

<button id="test">Start Test</button>
Results:<br />
<pre id="performance">Nothing yet...</pre>