How to check for null or undefined number but handle the zero value?

How to check for null or undefined number but handle the zero value?

HTML

<!DOCTYPE html>
<html>
<body>

<h1 style="background-color: red;">How to check for null or undefined number but handle the zero value?</h1>

<h3><a href="https://stackoverflow.com/q/75920528/2657515">https://stackoverflow.com/q/75920528/2657515</a></h3>

<br/>

<form onsubmit="return submitForm();">
<input id="input" value="0" /> &nbsp;
<input type="submit" value="Check" />
</form>
<pre><span id="output"></span></pre>

<script type="">
<!--

function submitForm() {
	var s = document.getElementById('input').value;
	var outputText ="";
    outputText += "<br/>Input is undefined/null/blank? <b>" + (isBlank(s) ? "Yes" : "No") + "</b>";
    outputText += "<br/>Input is zero?                 <b>" + (isZero(s)  ? "Yes" : "No") + "</b>";
	document.getElementById('output').innerHTML = outputText;
  document.getElementById('input').focus();
	return false;
}

function isBlank(s) {
	return (undefined == s || null == s || "" == s.trim());
}
function isZero(s) {
	return (!isBlank(s) && "0" == s.trim());
}

document.getElementById('input').focus();

-->
</script>

</body>
</html>