I would like to suggest to change the example in the JavaScript isNaN() Function topic (https://www.w3schools.com/jsref/jsref_isnan.asp) to the one below.
I have added parseFloat of every test example. It shows that sometimes isNaN returns false, but parseFloat returns NaN. Interesting might be also treatment of the date.
<!DOCTYPE html>
<html>
<body>
<p>The isNaN() function returns true if the value is NaN (Not-a-Number), and false if not.</p>
<p>Click the button to check whether a number is an illegal number.</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
function myFunction() {
var res = "";
res = res + isNaN(123) + ": 123 -> " + parseFloat(123) + "<br>";
res = res + isNaN(-1.23) + ": -1.23 -> " + parseFloat(-1.23) + "<br>";
res = res + isNaN(5-2) + ": 5-2 -> " + parseFloat(5-2) + "<br>";
res = res + isNaN(0) + ": 0 -> " + parseFloat(0) + "<br>";
res = res + isNaN('123') + ": '123' -> " + parseFloat('123') + "<br>";
res = res + isNaN('Hello') + ": 'Hello' -> " + parseFloat('Hello') + "<br>";
res = res + isNaN('2005/12/12') + ": '2005/12/12' -> " + parseFloat('2005/12/12') + "<br>";
res = res + isNaN('') + ": '' -> " + parseFloat('') + "<br>";
res = res + isNaN(true) + ": true -> " + parseFloat(true) + "<br>";
res = res + isNaN(undefined) + ": undefined -> " + parseFloat(undefined) + "<br>";
res = res + isNaN(null) + ": null -> " + parseFloat(null) + "<br>";
res = res + isNaN('NaN') + ": 'NaN' -> " + parseFloat('NaN') + "<br>";
res = res + isNaN(NaN) + ": NaN -> " + parseFloat(NaN) + "<br>";
res = res + isNaN(0 / 0) + ": 0 / 0 -> " + parseFloat(0 / 0) + "<br>";
document.getElementById("demo").innerHTML = res;
}
</script>
</body>
</html>