defer Attribute

Where to use the defer Attribute

• As Type Boolean:
  defer is declared on the element: script

Description

The defer attribute is a Boolean attribute which may be specified on a script element to indicate to the user agent that the script does not produce any document content and that page may finish loading before the script is executed.

This attribute has only partial support among user agents but, if you accept that it is merely a hint to the user agent and do not rely upon it, there's little harm in including it. If you need to use the DOM, for example, you should not assume that your document will have loaded before executing your deferred script. Use a JavaScript window.onload handler, for example, to make sure that you don't try to access the DOM before it's available.

See also the onload attribute.