JavaScript: GWT Basics: AJAX Programming with JavaScript

Prior to JavaScript and other client-side languages, Web browsers operated as if they were HTML dumb terminals, merely presenting Web pages generated on a server. For such pages, every user action requires a full page refresh, with a round-trip over the Internet, which degrades performance and thus user satisfaction. It may be fine for a great many Web sites, but it is completely inadequate for high-performance dynamic Web applications.