Essentials of Javascript - Cultural View

JavaScript 8
Example - use in web pages
A minimal example of a standards-conforming web page containing JavaScript (using HTML 4.01 syntax) would be
the following:
simple page
document.write('Hello World!');
Your browser either does not support JavaScript, or you have JavaScript turned off.
Compatibility considerations
Since JavaScript runs in widely varying environments, an important part of testing and debugging it is testing across
browsers.
The DOM interfaces for manipulating web pages are not part of the ECMAScript standard, or of JavaScript itself.
Officially, they are defined by a separate standardization effort by the W3C; in practice, browser implementations
differ from the standards and from each other, and not all browsers execute JavaScript.
To deal with these differences, JavaScript authors can attempt to write standards-compliant code which will also be
executed correctly by most browsers; failing that, they can write code that checks for the presence of certain browser
features and behaves differently if they are not available. [28] In some cases, two browsers may both implement a
feature but with different behavior, and authors may find it practical to detect what browser is running and change
their script's behavior to match. [29] [30] Programmers may also use libraries or toolkits which take browser
differences into account.
Furthermore, scripts may not work for some users. For example, a user may:
• use an old or rare browser with incomplete or unusual DOM support,
• use a PDA or mobile phone browser which cannot execute JavaScript,
• have JavaScript execution disabled as a security precaution,
• use a speech browser due to, for example, a visual disability.
To support these users, web authors can try to create pages which degrade gracefully on user agents (browsers)
which do not support the page's JavaScript. In particular, the page should remain usable albeit without the extra
features that the JavaScript would have added.