To convince yourself that JavaScript is at work in web applications such as Flickr, Google Maps, and Gmail, you can turn off JavaScript in your browser and see what changes in the behavior of the application.
To turn off JavaScript in your browser, do the following, depending on which browser you’re using:
In Firefox, uncheck Tools → Options → Content → Enable JavaScript.
In Internet Explorer, check Tools → Internet Options → Security → Custom Level → Scripting → Active Scripting → Disable.
In Opera, uncheck Tools → Quick Preferences → Enable JavaScript.
In Safari, uncheck Safari → Preferences → Security → Enable JavaScript.
Once you have JavaScript turned off, notice the following changes in Flickr and Google Maps:
In Flickr pages for a specific photo (in other words,
http://flickr.com/photos/{user-d}/{photo-id}/), you will see the
message “To take full advantage of Flickr, you should use a
JavaScript-enabled browser and install the latest version of the Macromedia
Flash Player.” All the buttons on top of the picture no longer function.
Instead of clicking the title, description, and tags to start editing them, you have
to click a link (Edit Title, Description, and Tags) before doing so.
Notice that some apps will gracefully support nonJavaScript-enabled browsers—particularly Google Maps. With JavaScript turned off, you no longer see the pan and zoom newstyle maps but an old-style map that provides links to move north, south, east, or west or to change the zoom level.
When using JavaScript, there are interesting and important issues regarding usability/accessibility. Many computers, including mobile devices, do not use JavaScript. How should apps gracefully deal with browsers that don’t use JavaScript? Some apps are so dependent on JavaScript that a non-JavaScript version would look drastically different.
Now that you have seen the effects of turning off JavaScript in the browser, be sure to turn it back on if you want to learn how to use JavaScript-based widgets and APIs.