MediaWiki:Common.js

$('.spoiler').click(
  function(e) {
    var $this, $next, hidden;
    $this = $(this);
    $next = $this.next();
    hidden = ($next.css('display') === 'none');
    $next.css('display', hidden ? 'inline-block' : 'none');
    $this.text(
        hidden ?
            $this.data('hide') || 'Hide' :
            $this.data('show') || 'Show'
    );
  }
);
$('.spoilerText').hide();