因为我总是想给浏览器一些有价值的东西，我经常使用这个技巧:

首先，页面中任何需要JavaScript才能正常运行的部分(包括通过getElementById调用等修改的被动HTML元素)都被设计成可用的，假设没有可用的JavaScript。(设计得好像它不存在一样)

任何需要JavaScript的元素，我在标签中放置如下内容:

<span name="jsOnly" style="display: none;"></span>

然后在文档的开头，使用.onload或document。在getElementsByName('jsOnly')的循环中设置.style。Display = "";重新打开JS依赖的元素。这样，非JS的浏览器就不需要看到站点中依赖于JS的部分，如果他们拥有它，它会在准备就绪时立即显示出来。

一旦您习惯了这种方法，就很容易混合您的代码来处理这两种情况，尽管我现在只是在试验noscript标记，并期望它会有一些额外的优点。

在meta noscript内部添加刷新不是一个好主意。

因为noscript标签不符合XHTML 属性值“Refresh”是非标准的，不应该使用。“刷新”将页面的控制权从用户手中夺走。使用“刷新”将导致W3C的Web内容可访问性指南失败 ——参考http://www.w3schools.com/TAGS/att_meta_http_equiv.asp。

因为我总是想给浏览器一些有价值的东西，我经常使用这个技巧:

首先，页面中任何需要JavaScript才能正常运行的部分(包括通过getElementById调用等修改的被动HTML元素)都被设计成可用的，假设没有可用的JavaScript。(设计得好像它不存在一样)

任何需要JavaScript的元素，我在标签中放置如下内容:

<span name="jsOnly" style="display: none;"></span>

然后在文档的开头，使用.onload或document。在getElementsByName('jsOnly')的循环中设置.style。Display = "";重新打开JS依赖的元素。这样，非JS的浏览器就不需要看到站点中依赖于JS的部分，如果他们拥有它，它会在准备就绪时立即显示出来。

一旦您习惯了这种方法，就很容易混合您的代码来处理这两种情况，尽管我现在只是在试验noscript标记，并期望它会有一些额外的优点。

我要在这里加上。02。虽然不是百分百防弹，但我觉得已经足够了。

对我来说，问题是，在我喜欢的例子中，提出一些“没有Javascript，这个网站不能很好地工作”的信息，然后你需要确保你的网站在没有Javascript的情况下也能正常工作。一旦你开始走上这条路，你就会开始意识到，关闭JS后，网站应该是防弹的，这是一大块额外的工作。

所以，你真正想要的是“重定向”到一个页面，上面写着“打开JS，傻瓜”。但是，当然，你不能可靠地做元重定向。所以，我的建议是:

<noscript>
    <style type="text/css">
        .pagecontainer {display:none;}
    </style>
    <div class="noscriptmsg">
    You don't have javascript enabled.  Good luck with that.
    </div>
</noscript>

.．.你站点中的所有内容都是用一个div类“pagcontainer”来包装的。noscript标签内的CSS将隐藏所有页面内容，而不是显示你想要显示的任何“无JS”消息。这实际上是Gmail所做的…如果它对谷歌来说足够好，它对我的小网站来说就足够好了。

下面是一个PHP脚本，它可以在生成任何输出之前包含一次。它不是完美的，但在大多数情况下，它工作得足够好，以避免交付客户端不会使用的内容或代码。标题注释解释了它是如何工作的。

<?php
/*****************************************************************************
 * JAVASCRIPT DETECTION                                                      *
 *****************************************************************************/

// Progressive enhancement and graceful degradation are not sufficient if we
// want to avoid sending HTML or JavaScript code that won't be useful on the
// client side.  A normal HTTP request will not include any explicit indicator
// that JavaScript is enabled in the client.  So a "preflight response" is
// needed to prompt the client to provide an indicator in a follow-up request.
// Once the state of JavaScript availability has been received the state of
// data received in the original request must be restored before proceding.
// To the user, this handshake should be as invisible as possible.
// 
// The most convenient place to store the original data is in a PHP session.
// The PHP session extension will try to use a cookie to pass the session ID
// but if cookies are not enabled it will insert it into the query string.
// This violates our preference for invisibility.  When Javascript is not
// enabled the only way to effect a client side redirect is with a "meta"
// element with its "http-equiv" attribute set to "refresh".  In this case
// modifying the URL is the only way to pass the session ID back.
//
// But when cookies are disabled and JavaScript is enabled then a client side
// redirect can be effected by setting the "window.onload" method to a function
// which submits a form.  The form has a "method" attribute of "post" and an
// "action" attribute set to the original URL.  The form contains two hidden
// input elements, one in which the session ID is stored and one in which the
// state of JavaScript availability is stored.  Both values are thereby passed
// back to the server in a POST request while the URL remains unchanged.  The
// follow-up request will be a POST even if the original request was a GET, but
// since the original request data is restored, the containing script ought to
// process the request as though it were a GET.

// In order to ensure that the constant SID is defined as the caller of this
// script would expect, call session_start if it hasn't already been called.
$session = isset($_SESSION);
if (!$session) session_start();

// Use a separate session for Javascript detection.  Save the caller's session
// name and ID.  If this is the followup request then close the caller's
// session and reopen the Javascript detection session.  Otherwise, generate a
// new session ID, close the caller's session and create a new session for
// Javascript detection.
$session_name = session_name();
$session_id = session_id();
session_write_close();
session_name('JS_DETECT');
if (isset($_COOKIE['JS_DETECT'])) {
    session_id($_COOKIE['JS_DETECT']);
} elseif (isset($_REQUEST['JS_DETECT'])) {
    session_id($_REQUEST['JS_DETECT']);
} else {
    session_id(sha1(mt_rand()));
}
session_start();

if (isset($_SESSION['_SERVER'])) {
    // Preflight response already sent.
    // Store the JavaScript availability status in a constant.
    define('JS_ENABLED', 0+$_REQUEST['JS_ENABLED']);
    // Store the cookie availability status in a constant.
    define('COOKIES_ENABLED', isset($_COOKIE['JS_DETECT']));
    // Expire the cookies if they exist.
    setcookie('JS_DETECT', 0, time()-3600);
    setcookie('JS_ENABLED', 0, time()-3600);
    // Restore the original request data.
    $_GET = $_SESSION['_GET'];
    $_POST = $_SESSION['_POST'];
    $_FILES = $_SESSION['_FILES'];
    $_COOKIE = $_SESSION['_COOKIE'];
    $_SERVER = $_SESSION['_SERVER'];
    $_REQUEST = $_SESSION['_REQUEST'];
    // Ensure that uploaded files will be deleted if they are not moved or renamed.
    function unlink_uploaded_files () {
        foreach (array_keys($_FILES) as $k)
            if (file_exists($_FILES[$k]['tmp_name']))
                unlink($_FILES[$k]['tmp_name']);
    }
    register_shutdown_function('unlink_uploaded_files');
    // Reinitialize the superglobal.
    $_SESSION = array();
    // Destroy the Javascript detection session.
    session_destroy();
    // Reopen the caller's session.
    session_name($session_name);
    session_id($session_id);
    if ($session) session_start();
    unset($session, $session_name, $session_id, $tmp_name);
    // Complete the request.
} else {
    // Preflight response not sent so send it.
    // To cover the case where cookies are enabled but JavaScript is disabled,
    // initialize the cookie to indicate that JavaScript is disabled.
    setcookie('JS_ENABLED', 0);
    // Prepare the client side redirect used when JavaScript is disabled.
    $content = '0; url='.$_SERVER['REQUEST_URI'];
    if (!$_GET['JS_DETECT']) {
        $content .= empty($_SERVER['QUERY_STRING']) ? '?' : '&';
        $content .= 'JS_DETECT='.session_id();
    }
    // Remove request data which should only be used here.
    unset($_GET['JS_DETECT'],$_GET['JS_ENABLED'],
            $_POST['JS_DETECT'],$_POST['JS_ENABLED'],
            $_COOKIE['JS_DETECT'],$_COOKIE['JS_ENABLED'],
            $_REQUEST['JS_DETECT'],$_REQUEST['JS_ENABLED']);
    // Save all remaining request data in session data.
    $_SESSION['_GET'] = $_GET;
    $_SESSION['_POST'] = $_POST;
    $_SESSION['_FILES'] = $_FILES;
    $_SESSION['_COOKIE'] = $_COOKIE;
    $_SESSION['_SERVER'] = $_SERVER;
    $_SESSION['_REQUEST'] = $_REQUEST;
    // Rename any uploaded files so they won't be deleted by PHP.  When using
    // a clustered web server, upload_tmp_dir must point to shared storage.
    foreach (array_keys($_FILES) as $k) {
        $tmp_name = $_FILES[$k]['tmp_name'].'x';
        if (move_uploaded_file($_FILES[$k]['tmp_name'], $tmp_name))
            $_SESSION['_FILES'][$k]['tmp_name'] = $tmp_name;
    }
// Have the client inform the server as to the status of Javascript.
?>
<!DOCTYPE html>
<html>
<head>
    <script>
        document.cookie = 'JS_ENABLED=1';
// location.reload causes a confirm box in FireFox
//      if (document.cookie) { location.reload(true); }
        if (document.cookie) { location.href = location; }
    </script>
    <meta http-equiv="refresh" content="<?=$content?>" />
</head>
<body>
    <form id="formid" method="post" action="" >
        <input type="hidden" name="<?=$session_name?>" value="<?=$session_id?>" />
        <input type="hidden" name="JS_DETECT" value="<?=session_id()?>" />
        <input type="hidden" name="JS_ENABLED" value="1" />
    </form>
    <script>
        document.getElementById('formid').submit();
    </script>
</body>
</html>
<?php
    exit;
}
?>

为什么需要知道服务器端是否启用了JavaScript ?浏览器支持哪种变体有关系吗?它是否需要理解关键字let或者只是var ?

我建议发送可读的内容，不需要任何JavaScript可访问，然后只是尝试加载JS文件添加所有你想要的JS行为。

For example, the UI might end up missing Login or Modify button if JS is not enabled and it might include a small text at the bottom (using <noscript> or some element with CSS animation that shows the text after a small delay if JS code doesn't remove the whole element soon enough) saying "To login/modify this content, you must enable JavaScript support in your browser." If you do this well, the reader may not even notice that anything is missing unless he or she is trying to login or modify the content.

作为一种优化，你可以用JavaScript设置cookie，如果你想异步获取它，服务器可以避免发送非JavaScript可读的内容。只是要确保在JS代码运行完成至少一次之后才设置这个cookie，而不是在JS代码开始运行时立即设置它，以确保当JS代码由于任何原因失败时(不是如果!)最终用户不会以空白屏幕结束。

(请注意，异步加载初始页面状态不会更快地将内容传递给最终用户。但是，如果没有JavaScript，您只能发送全部内容的一部分。这可以更快地呈现“优先”，然后使用JS代码异步加载页面的其余部分。)

作为一个额外的好处，搜索引擎仍然可以在不启用任何JavaScript的情况下索引您的站点。