docs: @Override
  	public boolean check(EmbeddedBrowser browser) {
  		String js =
  				"try{ if(" + expression + "){return '1';}else{" + "return '0';}}catch(e){"
  						+ " return '0';}";
  		try {
  			Object object = browser.executeJavaScript(js);
  			if (object == null) {
  				return false;
  			}
  			return object.toString().equals("1");
  		} catch (CrawljaxException e) {
  			// Exception is caught, check failed so return false;
  			return false;
  		}
  	}