JavaScript Features

JavaScript Features

JavaScript FAQ | Basic Syntax & General Questions

Question: What can JavaScript programs do?
Answer: The following list presents only some groups of typical tasks in which JavaScript proves very useful:

Giving the user more control over the browser
Detecting the user's browser, OS, screen size, etc.
Performing simple computations on the client side
Validating the user's input
Handling dates and time
Generating HTML code on-the-fly without accessing the Web server.
Below you'll find simple examples illustrating each of these tasks.
1. Giving the user more control over the browser.
Example: Here you can change the background color of this page as well as the text on the browser's status bar.

And here is a Back button implemented with JavaScript. Click it, and you'll return to the page from which you arrived:

2. Detecting the user's browser and OS. The ability to detect the user's browser and OS allows your script to perform platform-dependent operations, if necessary.
Example. Here users of different browsers will get different greetings:

3. Performing simple computations on the client side.
Example. This is a JavaScript calculator: type an arithmetic expression, and JavaScript will compute its value.

4. Validating the user's input.
Example. In the calculator above, try typing some letters instead of numeric input. You'll get a warning: Invalid input characters!
Note that JavaScript helps the browser perform input validation without wasting the user's time by the Web server access. If the user makes a mistake in the input, the user will get an error message immediately! On the other hand, if the input information is validated only on the server, then the user would have to wait for the server response.
5. Handling dates and time.
Example 1. This is a JavaScript clock.
Local time:

Example 2. This script says "Nice morning, isn't it?" or "Good afternoon!" or "Good evening!" or "Wow, you are not asleep yet!?" depending on the current time. It also tells you today's date.

6. Generating HTML on the fly.
Example. is dynamically expandable. To view all subsections in a section, you can click on the white arrow corresponding to that section. To hide subsections, click on the arrow .
Every time you click on the arrows, the browser generates and displays new HTML code in the left frame. Thanks to JavaScript, this operation is performed on the client machine, and therefore you don't have to wait while the information goes back and forth between your browser and the Web server.