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JavaScript - IsNan

The isNaN() function determines whether a value is an illegal number (Not-a-Number). This function returns true if the value equates to NaN. Otherwise it returns false. 


// example
var x = 100 / "Apple";
isNaN(x); // returns true because x is Not a Number

Enter a number between 1 and 100.


function ValidateNumber()
{
    let num = document.getElementById("txtNumber").value;
    let message = "";
    let demo = document.getElementById("demo1");

    if (isNaN(num) || num === "")
    {
        message = "This is not a number.";
    }
    else if ((num < 0) || (num> 100))
    {
        message = "This number is not between 1 and 100.";
    }
    else
    {
        message = "Your number of " + num + " is valid.";
    }

    demo1.innerHTML = message;
}