function changMainTab(onTab) {

    var tabName = ['mainTab1', 'mainTab2'];

    for (i=0; i<2; i++) {
        if (tabName[i] == onTab) {
            document.getElementById(tabName[i]).style.display = "block";
        } else {
            document.getElementById(tabName[i]).style.display = "none";
        }
    }
    
}