Learning JavaScript

What You Can Do with JavaScript

JavaScript achieved early widespread use for simple tasks: validating form contents, or setting and retrieving cookies (small bits of information that persist even when the browser is closed). In the late 1990s, with the introduction of Dynamic HTML (DHTML), JavaScript was also used to provide a more dynamic user experience through drop-down menus and the like.

JavaScript’s popularity has grown—exploded, really—most recently because it is a key component in Ajax (Asynchronous JavaScript and XML), which promises to restructure the way web applications interact with users. Over time, many cross-platform problems have been resolved, and the language has become more sophisticated—so much so that JavaScript is no longer just a scripting language; it’s a full-featured programming language.

So what can you do with JavaScript? Well, for starters:

Validate form fields

Validate form input before submitting the contents to the server. This saves time and server resources, and provides immediate feedback.

Set and retrieve web cookies

Persist information such as usernames, account numbers, or preferences in a controlled, safe environment—saving users time the next time they access a site.

Dynamically alter the appearance of a page element

Provide feedback by highlighting incorrect form entries; increase the size of a section’s font based on the reader’s request.

Hide and show elements

Based on personal preference or user actions, show or hide page content, such as form ...