Maxlength checking in Textarea Using Javascript

function maxcheck()
{
var maxval=1000;
var maxtxtlength=window.document.myform.Description.value.length;
if(parseInt(maxtxtlength)>parseInt(maxval))
{
alert("This Description field accept only 1000 characters");
window.document.myform.Description.innerText=window.document.myform.Description.value.substring(0,1000);
return false;
}
}