Cycle Through Visual Event Bookmarklet Layers

gistfile1.js

// Code I paste into the Firebug Console after I run the Visual Event
// bookmarklet (http://www.sprymedia.co.uk/article/Visual+Event)
// so I can cycle through the layers - Use arrow keys to cycle

var veColors = [ 'black', 'orange', 'purple', 'green', 'blue', 'yellow', 'red' ],
 veColorLength= veColors.length - 1,
 veLayerIndex = 0;
 
function showVeLayer(nxt){
 veLayerIndex += (nxt) ? 1 : -1;
 if (veLayerIndex > veColorLength) { veLayerIndex = 0; }
 if (veLayerIndex < 0) { veLayerIndex = veColorLength; }

 var veLayer =  $('.Event_bg_' + veColors[veLayerIndex]);
 if (veLayer.length === 0 ) { showVeLayer(nxt); return; }

 $('.Event_bg_' + veColors.join(', .Event_bg_')).hide();
 veLayer.show();
};

$(document).keyup(function(e){
 switch(e.which){
  case 39: case 40: // right/down
   showVeLayer(true);
   break;
  case 37: case 38: // left/up
   showVeLayer();
   break;
 }
});