var tCactive;
var tCobj;
var tCcheckLength;
function startCheckTextarea(objInput, length) {
    tCobj = objInput;
    tCcheckLength = length;
    tCactive = window.setInterval("doCheck()", 500);

}
function doCheck() {
    if (tCobj.value && tCobj.value.length > tCcheckLength) {
        window.clearInterval(tCactive);
        tCobj.value = tCobj.value.substring(0, tCcheckLength);
        alert("Sie können hier nur max. " + tCcheckLength + " Zeichen eingeben.");
        tCobj.focus();

    }

}
function endCheckTextarea() {
    window.clearInterval(tCactive);
}