Chapter 1. Purpose

The purpose of JavaScript is to add an extra layer of usability to a Web page.

That sounds simple, but this golden rule has frequently been misunderstood. Not all scripts add usability to a Web site; in fact, during several periods of JavaScript’s checkered history, the creation of flashy-looking but useless scripts has been a significant cottage industry.

Even when writing useful scripts, JavaScript developers haven’t always written them in their proper context: that of an accessible, modern HTML page that integrates the insights of the Web standards movement.

Worse, some scripts don’t add a usability layer, they are the entire usability layer—and as a consequence the site falls apart when a browser doesn’t support JavaScript. ...

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