How To Use Javascript to Get Field Value From Another List?

Salvete! How do I use javascript to fetch a value from a custom list that is not loaded in the browser?

This post seems relevant, but it fetches values from a list that is loaded.

From that post, I have created this, but I can't get it to show any alerts or log anything in the console. I can't say I understand exactly what is going on, however - delegates are shaky ground for me, and I am just learning the sp functions.

spload("getFields('Retreats', 'Capacity')");   //this is how I am calling the function

function spload(whatfunction){    //waits until sharepoint is ready
    _spBodyOnLoadFunctionNames.push(whatfunction);
}

function getFields(listName, whatcolumn){
  var context = new SP.ClientContext.get_current();
  var web = context.get_web();
  var lists = web.get_lists();
  //var listId = SP.ListOperation.Selection.getSelectedList();
  //var list = lists.getById(listId);
  var list = web.get_lists().getByTitle(listName); 
  var selectedItems = SP.ListOperation.Selection.getSelectedItems();  //<-- IS THIS RIGHT?  If my list is not loaded, how can there be any selected items?

  this.items = [];
  for (var i in selectedItems) {
    var id = selectedItems[i].id;
    var item = list.getItemById(id);
    items.push(item);
    context.load(item, whatcolumn);
  }
  context.executeQueryAsync(Function.createDelegate(this, getAndShowTitle),
    Function.createDelegate(this, showError));
}
function getAndShowTitle() {
    for (var item in items) {
        console.log(item.get_item(whatcolumn));
        alert(item.get_item(whatcolumn));
    }
}
function showError(sender, args) {
  alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}

[update]

Now, notice this line:

 var selectedItems = SP.ListOperation.Selection.getSelectedItems(); 

If the list isn't loaded, how can there be any selected item?