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HTML <script> Tag

The HTML <script> tag declares client-side script (JavaScript) in an HTML document. When defining a client-side script the script tag is used for image manipulation, form validation, and dynamic changes of content. The tag can include either the script itself or a link to an external file containing scripts.The path to the external file is specified with src attribute.

If you connect an external file with scripts, don’t embed script into the same <script> tag.

The HTML <script> tag can be placed in the <head> element, as well as within the <body> element. The script execution doesn’t depend on its location in an HTML document, but the scripts, that must be executed first, must be placed in the heading of the document. The <script> tag can be used in an HTML document many times.

Syntax

The <script> tag comes in pairs; the closing tag (</script>) is required.

Important notes

There are a few ways an external script can be executed:

  • The async="async" attribute indicates, that the scripts are executed asynchronously, simultaneously with the loading of the page.
  • When there is no async and defer="defer", the script is executed after the loading of the page.
  • If there is no async and defer, the script is executed before the loading of the page.

For selecting an HTML element, JavaScript uses the document.getElementById() method.

Example of HTML <script> tag:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
  </head>
  <body>
    <p id="example"></p>
    <script>
      document.getElementById("example").innerHTML = "My first JavaScript code";
    </script>
  </body>
</html>

Differences Between HTML 4.01 and HTML5

HTML 4 requires the type attribute, whereas it is optional in HTML5. In HTML5, the async attribute is a new one. HTML5 does not support the HTML 4.01 xml:space attribute.

Differences Between HTML and XHTML

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

In XHTML, all special characters should be encoded, or all content should be wrapped inside a CDATA section.

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

Attributes

Attribute Value Description
async async Defines that the script is executed asynchronously. (For external scripts only).
Not supported in IE9 and older versions.
charset charset Defines character encoding, used in an external file with the JavaScript code.
defer defer Defines, that the script must be executed after the loading of the page. (For external scripts only).
src URL Defines the URL of an external file with the JavaScript code. (Can be defined either relative, or an absolute URL).
type media_type Defines the MIME-type of the script.

The <script> tag supports the Global Attributes and the Event Attributes.


Browser support



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