HTML <script> Tag


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Definition and Usage

The <script> tag is used to define a client-side script (JavaScript).

The <script> element either contains scripting statements, or it points to an external script file through the src attribute.

Common uses for JavaScript are image manipulation, form validation, and dynamic changes of content.

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Browser Support

<script> Yes Yes Yes Yes Yes Yes

Tips and Notes

Note: If the "src" attribute is present, the <script> element must be empty.

Tip: Also look at the <noscript> element for users that have disabled scripts in their browser, or have a browser that doesn't support client-side scripting.

Note: There are several ways an external script can be executed:

  • If async="async": The script is executed asynchronously with the rest of the page (the script will be executed while the page continues the parsing)
  • If async is not present and defer="defer": The script is executed when the page has finished parsing
  • If neither async or defer is present: The script is fetched and executed immediately, before the browser continues parsing the page

Differences Between HTML 4.01 and HTML5

The "type" attribute is required in HTML 4, but optional in HTML5.

The "async" attribute is new in HTML5.

The HTML 4.01 attribute: "xml:space", is not supported in HTML5.

Differences Between HTML and XHTML

In XHTML, the content inside scripts is declared as #PCDATA (instead of CDATA), which means that entities will be parsed.

This means that in XHTML, all special characters should be encoded, or all content should be wrapped inside a CDATA section:

<script type="text/javascript">
var i = 10;
if (i < 5) {
  // some code