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HTML defer Attribute

The HTML defer attribute specifies that a script is executed when a page has finished the parsing. Read and find out how to use it on the <script> element.

The HTML defer attribute specifies that a script is executed when a page has finished the parsing. It is a boolean attribute. This attribute works for external scripts and must be used only when the src attribute is present.

In HTML 4.01, the behavior of the defer attribute was implementation-dependent, whereas HTML5 standardized it. In XHTML, the defer attribute must be specified as <script defer="defer"> as attribute minimization is forbidden.

You can use this attribute on the <script> element.

An external script can be executed in the following ways:

  • When async is present, the script will be executed asynchronously while the page continues the parsing.
  • When async is not present but defer is present, the script will be executed when the page finishes the parsing, in the order they appear in the document.
  • When neither async nor defer is present, the script will be executed immediately before the browser continues the parsing.

Syntax

Syntax of HTML defer Attribute

<script src="example.js" defer></script>

Example of the HTML defer attribute:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <script src="example.js" defer></script>
    <noscript>Sorry, your browser doesn't support JavaScript!</noscript>
  </head>
  <body>
    <h1>Example</h1>
    <p>The "defer" attribute specifies that a script is executed when a page has finished the parsing. It is a boolean attribute.</p>
  </body>
</html>
Try it Yourself »

Practice

Practice

What is the correct use of the 'defer' attribute in HTML?