What is JavaScript?
I recommend using ECMAScript instead of JavaScript.
JavaScript is NOT Java, but a scripting language developed by Netscape Communications to add interactivity to Web pages. JavaScript is written into an HTML file. A JavaScript-aware browser can interpret JavaScript code and provide a variety of interactive animations or actions on the Web page.
What is the Big Deal About JavaScript?
Before the dawn of the Java Age (1995), most Web pages were static: a page of text with perhaps some hyperlinks or an imagemap which you could "click." Click. Click. Got pretty boring. The idea of Java was that interactivity could be added to Web pages. Sun Microsystems invented Java. Netscape Communications ripped them off by naming an unrelated technology with a similar name: JavaScript, and people have been confused ever since.
JavaScript adds client-side interactivity to Web pages without requiring a great deal of programming. As such, it is useful for doing small, specific tasks on Web pages.