Unobtrusive JavaScript

Unobtrusive JavaScript is a general approach to the use of JavaScript in web pages. Though the term is not formally defined, its basic principles are generally understood to include:

JavaScript historically has had a reputation for being a clumsy language unsuitable for serious application development. This has been largely due to inconsistent implementations of the language itself and the Document Object Model (DOM) in various browsers, and the widespread use of buggy copy-and-paste code. Runtime errors were so common (and so difficult to debug) that few programmers ever tried to fix them, as long as the script behaved more or less the way it was supposed to; scripts often failed completely in some browsers.

Some web developers have been promoting graceful degradation since 1994.

The recent emergence of standards-compliant browsers, JavaScript frameworks and high-quality debugging tools have made organized, scalable JavaScript code possible, and the emergence of Ajax interfaces has made it desirable. Whereas JavaScript was once reserved for relatively simple and non-critical tasks such as form validation and decorative novelties, it is now being used to write large, complex codebases that are often part of a site's core functionality. Run time errors and unpredictable behavior are no longer minor annoyances; they are fatal flaws.

Advocates of unobtrusive JavaScript see it as part of the larger Web standards movement; much as the demand for cross-browser compatibility has driven the increasing emphasis on standardized markup and style, the increasing demand for rich Internet applications is driving the movement toward better practices with the use of JavaScript. The concept of unobtrusiveness in relation to JavaScript programming was coined in 2002 by Stuart Langridge in the article "Unobtrusive DHTML, and the power of unordered lists". In the article Langridge argues for a way to keep all JavaScript code, including event handlers, outside of the HTML. Stuart Langridge has since expanded upon this thought in book and article format.

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