function addToCounter(number) {
    var spanPageCounter = document.getElementById('SpanPageCounter');
    var counter = parseInt(spanPageCounter.innerHTML);
    counter = number + counter;
    spanPageCounter.innerHTML = counter;
}
function resetCounter() {
    var spanPageCounter = document.getElementById('SpanPageCounter');
    spanPageCounter.innerHTML = 0;
}
function setCounter(number) {
    var spanPageCounter = document.getElementById('SpanPageCounter');
    spanPageCounter.innerHTML = number;
}
function getCounter() {
    var spanPageCounter = document.getElementById('SpanPageCounter');
    var counter = parseInt(spanPageCounter.innerHTML);
    return counter;
}