var W3CDOM = document.createElement && document.getElementsByTagName;

function setMaxLength() {
    if (!W3CDOM) return;
    var textareas = document.getElementsByTagName('textarea');
    var counter = document.createElement('div');
    counter.className = 'counter';
    for (var i=0;i<textareas.length;i++) {
        if (textareas[i].getAttribute('maxlength')) {
            var counterClone = counter.cloneNode(true);
            counterClone.innerHTML = '<span>0</span>/'+textareas[i].getAttribute('maxlength');
            textareas[i].parentNode.insertBefore(counterClone,textareas[i].nextSibling);
            textareas[i].relatedElement = counterClone.getElementsByTagName('span')[0];
            textareas[i].onkeyup = textareas[i].onchange = checkMaxLength;
            textareas[i].onkeyup();
        }
    }
}

function checkMaxLength() {
    var maxLength = this.getAttribute('maxlength');
    var currentLength = this.value.length;
    if (currentLength < 3) {
        $('#minknapp').attr("disabled", true);
    }
    if (currentLength > maxLength) {
        $('#minknapp').attr("disabled", true);
        this.relatedElement.className = 'maxlen';
    } else {
        this.relatedElement.className = ''; 
        $('#minknapp').attr("disabled", false);
    }
    this.relatedElement.firstChild.nodeValue = currentLength;
}