Function To Validate Only Number Allowed in JavaScript

function fnNotAlphabet(e)
{
    var code = e.keyCode ? event.keyCode : e.which ? e.which : e.charCode;       
    //Code Explanation{ 0-9, 45=Insert, 13=Enter, 08=Backspace, 09=Tab}
    if ((code >= 48 && code <= 57)||(code == 45 || code == 13 || code == 08 || code == 09))
    {
        checknos = true;
        return (checknos);
    }
    else
    {
        checknos= false;
        alert("Only Number Allowed !");   
        return (checknos);
    }
}