|Contents||An embedded script|
|Contained in||HEAD, block-level elements, inline elements except SELECT and SCRIPT|
The SCRIPT element includes a client-side script in the document. Client-side scripts allow greater interactivity in a document by responding to user events. For example, a script could be used to check the user's form input prior to submission to provide immediate notice of any errors by the user.
Note that not all browsers support client-side scripting, and supporting browsers allow the user to disable scripting. In particular, browsers on mobile phones often ship with scripting disabled for performance reasons. Authors should avoid dependence on client-side scripting wherever possible. The NOSCRIPT element can be used to provide content for browsers that do not support client-side scripting or have it disabled. In the case of form validation, any error checking done by the client-side script should be repeated by the server-side form processor.
Also note that different browsers support different variants of scripting languages with different bugs. Authors are encouraged to check their scripts on as many browsers as possible.
An embedded script is given as the content of the SCRIPT element. The SRC attribute allows authors to reuse code by specifying an external script. The optional CHARSET attribute gives the character encoding of the external script, although this attribute is rarely needed in practice. When the SRC attribute is used, the embedded script is ignored. An example follows:
<!-- // embedded script ignored // -->
The DEFER attribute indicates that the browser may wait to parse the script until the rest of the document has been rendered. Scripts that use DEFER must not generate any document content, and should not be required to respond to user events (e.g., form submission) that may occur while the document is loading. The DEFER attribute can be useful for delaying scripts that pre-load images or harass the user with scrolling messages in the status bar.
The SCRIPT element may occur any number of times in the document HEAD or BODY. Typically the SCRIPT element is used in the HEAD unless it generates BODY content.
Pre-HTML 3.2 browsers, unaware of the SCRIPT element, will treat the content of SCRIPT as normal HTML. To make these browsers ignore the SCRIPT's content, scripting languages generally allow SGML comments to be used around an embedded script. For example:
<!-- comment to end of line document.write("foo"); // comment to end of line -->