On getting the result of the following, you can find whether a variable is null or undefined. If the result is “false”, it means the variable is null and undefined.
Here, the variable results in “True” −
<html>
<body>
<script>
var age = 10;
if(age) {
document.write("True");
} else {
document.write("False");
}
</script>
</body>
</html>