The DocumentFragment.querySelector() method returns the first element, or null if no matches are found, within the DocumentFragment (using depth-first pre-order traversal of the document's nodes) that matches the specified group of selectors.

If the selector matches an ID and this ID is erroneously used several times in the document, it returns the first matching element.

If the selectors specified in parameter are invalid a DOMException with a SYNTAX_ERR value is raised.

selectors

A string containing one or more CSS selectors separated by commas.

An Element object representing the first element in the document that matches the specified set of CSS selectors, or null is returned if there are no matches.

In this basic example, the first element in the DocumentFragment with the class "myclass" is returned:

const el = documentfragment.querySelector(".myclass");

The string argument pass to querySelector must follow the CSS syntax. To match ID or selectors that do not follow the CSS syntax (by using semicolon or space inappropriately for example), it's mandatory to escape the wrong character with a double back slash:

<div id="foo\bar"></div>
<div id="foo:bar"></div>

<script>
  document.querySelector("#foo\bar"); // Does not match anything
  document.querySelector("#foo\\\\bar"); // Match the first div
  document.querySelector("#foo:bar"); // Does not match anything
  document.querySelector("#foo\\:bar"); // Match the second div
</script>

• The DocumentFragment interface it belongs to.