// Number of submenus
var NumberOfMenus = 6;

// Submenu Array
var SubMenu = [];
for ( var i = 0; i < NumberOfMenus ; i++ ) {
  SubMenu[i] = "menu"+(i+1);
}

// Currently visible menuitem
var currentSubMenu = 0;

// Hide all submenus
function hideSubMenus() {
  for ( var i=0; (i<NumberOfMenus); i++ ) {
    var menuobj = document.getElementById(SubMenu[i]);
    menuobj.style.display="none";
  }

} 

// Show submenu function
function showSubMenu( menuId ) {
  
  // Set current menu invisible
  var menuObj = document.getElementById(SubMenu[currentSubMenu]);
  currentSubMenu=(menuId-1);
  menuObj.style.display="none";
  
  // Set new menu visible
  menuObj = document.getElementById(SubMenu[(menuId-1)]);
  menuObj.style.display="block";

}