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 before() method of the DocumentType interface inserts a set of Node objects or strings in the children list of this DocumentType's parent, just before this DocumentType. Strings are inserted as equivalent Text nodes. Nothing happens if parentNode is null.
Syntax
js
before(param1)
before(param1, param2)
before(param1, param2, /* …, */ paramN)
Parameters
param1, …,paramN-
A set of
Nodeobjects or strings to insert.
Return value
None (undefined).
Exceptions
HierarchyRequestErrorDOMException-
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:
js
const docType = document.implementation.createDocumentType("html", "", "");
const 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 |