JavaScript: The Definitive Guide, Fourth Edition

Compatibility with Non-JavaScript Browsers

The previous section discussed compatibility with browsers that do not support a particular version of JavaScript. This section considers compatibility with browsers that do not support JavaScript at all. These are either browsers that have no JavaScript capability or browsers in which the user has disabled JavaScript (which some users do because of security concerns). Because a number of such browsers are still in use, you should design your web pages to fail gracefully when read into browsers that do not understand JavaScript. There are two parts to doing this: first, you must take care to ensure that your JavaScript code does not appear as if it were HTML text; and second, you should arrange to display a message informing the visitor that her browser cannot correctly handle the page.

Hiding Scripts from Old Browsers

Web browsers that support JavaScript execute the JavaScript statements that appear between the <script> and </script> tags. Browsers that don’t support JavaScript but recognize the <script> tag simply ignore everything between <script> and </script>. This is as it should be. Really old browsers, however (and there are still some out there), do not even recognize the <script> and </script> tags. This means that they ignore the tags themselves and treat all the JavaScript between them as HTML text to be displayed. Unless you take steps to prevent it, users of these old browsers see your JavaScript code formatted into big ...