To check if a variable is an integer, check the value using parseInt() and check with === operator.
Example
You can try to run the following code to check the existence of an integer −
<html>
<head>
<script>
var a = 10;
if (a === parseInt(a, 10))
alert("Integer!")
else
alert("Not an integer!")
</script>
</head>
<body>
</body>
</html>