supports maxLength-limitations to textarea in prototypejs

prototypejs-maxlength.js

Element.addMethods(["textarea"], {
    /**
     * @description supports maxLength-limitations to textarea;
     * @param element
     * @param max charset length in field
     * @param handler a handler-function which have the current left charset value in parameter
     */
    maxTextLength: function(element, max, handler){
        element = $(element);
        handler = (handler == undefined) ? function(){} : handler;
        var checkLength = function(){
            if( this.value.length >= max ) {
                this.value = element.value.substring(0, max);
                handler(0);
            } else {
                handler(max - this.value.length);
            }
        };
        element.observe('keyup', checkLength.bindAsEventListener(element));
        checkLength.bindAsEventListener(element);
        return element;

    }
});