<!DOCTYPE html>
<title>isPrimeNumber</title>
<div>Expected value: <b>true</b></div>
<div>Actual value: <b id="ret"></b></div>
<script>
var myFunction = function(a){return!/^,?$|^(,,+)\1+$/.test(Array(-~a))};
document.getElementById( "ret" ).innerHTML = myFunction(541)
</script>