selenium webdriver 执行Javascript

    @Test
    public void testElementByID()
    {
        //通过JS获取页面元素
        driver.get(url);
        driver.manage().window().maximize();
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        String js = "var user_input = document.getElementById("su").value;return user_input;"; 
        String content=(String) ((JavascriptExecutor)driver).executeScript(js);
        System.out.println(content);
        Assert.assertEquals( "百度一下", content);
        driver.quit();
    }