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DocumentType: before() method

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨April 2018⁩.

The DocumentType.before() method inserts a set of Node objects or strings in the children list of the DocumentType's parent, just before the DocumentType. Strings are inserted as equivalent Text nodes.

Syntax

before(param1)
before(param1, param2)
before(param1, param2, /* …, */ paramN)

Parameters

param1, …, paramN: A set of Node objects or strings to insert.

Return value

None (undefined).

Exceptions

HierarchyRequestError DOMException: Thrown when the node cannot be inserted at the specified point in the hierarchy.

Examples

Adding a conditional comment

Comment nodes are valid before doctype declarations but not advisable given they trigger quirks mode in IE. A conditional comment works for IE as well, though:

let docType = document.implementation.createDocumentType("html", "", "");
let myDoc = document.implementation.createDocument("", "", docType);

docType.before(
  document.createComment("<!--[if !IE]> conditional comment <![endif]-->"),
);

myDoc.childNodes;
// NodeList [<!--[if !IE]> conditional comment <![endif]-->, <!DOCTYPE html>]

Specifications

Specification
DOM> # ref-for-dom-childnode-before①>

Browser compatibility

	Desktop					Mobile
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	WebView on iOS
`before`	54	17	49	39	10	54	49	41	10	6.0	54	10