textArea controlar cantidad caracteres

//funcion javascript

 function ValidarCaracteres(textareaControl, maxlength) {

            if (textareaControl.value.length > maxlength) {
                textareaControl.value = textareaControl.value.substring(0, maxlength);
            }

//propiedad en el textbox
onkeypress="ValidarCaracteres(this,200);" onkeyup="ValidarCaracteres(this,200);"