How to check whether a number is NaN in javascript?

Html page:

<button onclick="myFunction()">Try it</button>

<p id="P7"></p>

Javascript page:

<script>

    function myFunction() {

        var res = "";

        res = res + Number.isNaN(123) + ": 123<br>";

        res = res + Number.isNaN(-1.23) + ": -1.23<br>";

        res = res + Number.isNaN(5 - 2) + ": 5-2<br>";

        res = res + Number.isNaN(0) + ": 0<br>";

        document.getElementById("demo").innerHTML = res;

    }

</script>

Output:

false: 123

false: -1.23

false: 5-2

false: 0