How Is element.querySelector different than document.querySelector?

The querySelector() returns the first element within the document that matches the selector(s) and null if no match is found. This will only return the first element that matches the selectors. You need to use a different method to return all matches, querySelectorAll()

Element: querySelector() method

The querySelector() method of the Element interface returns the first element that is a descendant of the element on which it is invoked that matches the specified group of selectors.

Syntax

querySelector(selectors)

Parameters

selectors: A group of selectors to match the descendant elements of the Element baseElement against; this must be valid CSS syntax, or a SyntaxError exception will occur. The first element found which matches this group of selectors is returned.

Return value

The first descendant element of baseElement which matches the specified group of selectors. The entire hierarchy of elements is considered when matching, including those outside the set of elements including baseElement and its descendants; in other words, selectors is first applied to the whole document, not the baseElement, to generate an initial list of potential elements. The resulting elements are then examined to see if they are descendants of baseElement. The first match of those remaining elements is returned by the querySelector() method.

If no matches are found, the returned value is null.

Exceptions

SyntaxError DOMException: Thrown if the specified selectors are invalid.

Examples

Let's consider a few examples.

Find a specific element with specific values of an attribute

In this first example, the first <style> element which either has no type or has type "text/css" in the HTML document body is returned:

const el = document.body.querySelector(
  "style[type='text/css'], style:not([type])",
);

Get direct descendants using the :scope pseudo-class

This example uses the :scope pseudo-class to retrieve direct children of the parentElement element.

HTML

<div>
  <h6>Page Title</h6>
  <div id="parent">
    <span>Love is Kind.</span>
    <span>
      <span>Love is Patient.</span>
    </span>
    <span>
      <span>Love is Selfless.</span>
    </span>
  </div>
</div>

CSS

span {
display: block;
 margin-bottom: 5px;
}
.red span {
  background-color: red;
  padding: 5px;
}

JavaScript

const parentElement = document.querySelector("#parent");
let allChildren = parentElement.querySelectorAll(":scope > span");
allChildren.forEach((item) => item.classList.add("red"));

Result

Page Title
Love is Kind.
Love is Patient
Love is Selfless.

The entire hierarchy counts

This example demonstrates that the hierarchy of the entire document is considered when applying selectors, so that levels outside the specified baseElement are still considered when locating matches.

HTML

<div>
  <h5>Original content</h5>
  <p>
    inside paragraph
    <span>inside span</span>
    inside paragraph
  </p>
</div>
<div>
  <h5>Output</h5>
  <div id="output"></div>
</div>

JavaScript

const baseElement = document.querySelector("p");
document.getElementById("output").innerHTML =
  baseElement.querySelector("div span").innerHTML;

Result

The result looks like this:

Original content
inside paragraph inside span inside paragraph

Output
inside span

Notice how the "div span" selector still successfully matches the <span> element, even though the baseElement's child nodes do not include the <div> element (it is still part of the specified selector).

Source: Mozilla, https://developer.mozilla.org/en-US/docs/Web/API/Element/querySelector
This work is licensed under a Creative Commons Attribution-ShareAlike 2.5 License.

Last modified: Monday, July 17, 2023, 4:25 AM