var image_container = {};

window.onload = function() {
  var images = ['home','productions','tickets','howhelp','fromdirect','about','donate'];
  var base_uri = '/images/nav/';
  
  for (var i in images) {
    var image = images[i];
    var id = images[i] + '_nav';
    
    image_container[id] = []
    image_container[id][1] = new Image();
    image_container[id][1].src = base_uri + image + '_on.gif';
    image_container[id][0] = new Image();
    image_container[id][0].src = base_uri + image + '.gif';
    
    if (document.getElementById(id)) {
      document.getElementById(id).onmouseover = function() {
        swap(this, 1);
      }
      
      document.getElementById(id).onmouseout = function() {
        swap(this, 0);
      }
    }
  }
}

function swap(e, onoff) {
  e.firstChild.src = image_container[e.id][onoff].src;
}