To Validate Only Digits Using JavaScript

//To accept only Digits
//Use this function at the time of keyup

function isDigit(evt)
{
    var charCode = (evt.which) ? evt.which : event.keyCode
    if (charCode > 47 && charCode < 58)
    {	
	    return true;
    }
	else
	{			
	    return false;
        }       
}