The isNaN() function is used to determine whether variable is a valid number.
<html> <body> <script lanuguage="JavaScript"> <!-- function checkNum(){ var n = document.form1.text1.value; if(isNaN(n) == true){ alert("Your entry is not a number"); }else{ alert("Your entry is a number"); } } --> </script> <form name="form1"> Enter a number or character into the text box and then click the check value button to verify if the input is a number. <br><br> <input type="text" name="text1" size=3> <br><br> <input type="button" value="Check value" onClick='checkNum()'> <br> </form> </body> </html>
