TreeWalker

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨July 2015⁩.

The TreeWalker object represents the nodes of a document subtree and a position within them.

A TreeWalker can be created using the Document.createTreeWalker() method.

Instance properties

This interface doesn't inherit any property.

TreeWalker.root Read only: Returns the root Node as specified when the TreeWalker was created.
TreeWalker.whatToShow Read only: Returns an unsigned long which is a bitmask made of constants describing the types of Node that must be presented. Non-matching nodes are skipped, but their children may be included, if relevant.
TreeWalker.filter Read only: Returns the NodeFilter associated with this TreeWalker used to select the relevant nodes.
TreeWalker.currentNode: Is the Node on which the TreeWalker is currently pointing at.

Instance methods

This interface doesn't inherit any method.

Note: In the context of a TreeWalker, a node is visible if it exists in the logical view determined by the whatToShow and filter parameter arguments. (Whether or not the node is visible on the screen is irrelevant.)

TreeWalker.parentNode()

Moves the current Node to the first visible ancestor node in the document order, and returns the found node. It also moves the current node to this one. If no such node exists, or if it is before that the root node defined at the object construction, returns null and the current node is not changed.

TreeWalker.firstChild()

Moves the current Node to the first visible child of the current node, and returns the found child. It also moves the current node to this child. If no such child exists, returns null and the current node is not changed. Note that the node returned by firstChild() is dependent on the value of whatToShow set during instantiation of the TreeWalker object. Assuming the following HTML tree, and if you set the whatToShow to NodeFilter.SHOW_ALL a call to firstChild() will return a Text node and not an HTMLDivElement object.

html

<!doctype html>
<html lang="en">
 <head>
 <title>Demo</title>
 </head>
 <body>
 <div id="container"></div>
 </body>
</html>

let walker = document.createTreeWalker(document.body, NodeFilter.SHOW_ALL);
let node = walker.firstChild(); // nodeName: "#text"

But if we do:

let walker = document.createTreeWalker(
 document.body,
 NodeFilter.SHOW_ELEMENT,
);
let node = walker.firstChild(); // nodeName: "DIV"

The same applies to nextSibling(), previousSibling(), firstChild() and lastChild()

TreeWalker.lastChild()

Moves the current Node to the last visible child of the current node, and returns the found child. It also moves the current node to this child. If no such child exists, null is returned and the current node is not changed.

TreeWalker.previousSibling()

Moves the current Node to its previous sibling, if any, and returns the found sibling. If there is no such node, return null and the current node is not changed.

TreeWalker.nextSibling()

Moves the current Node to its next sibling, if any, and returns the found sibling. If there is no such node, null is returned and the current node is not changed.

TreeWalker.previousNode()

Moves the current Node to the previous visible node in the document order, and returns the found node. It also moves the current node to this one. If no such node exists, or if it is before that the root node defined at the object construction, returns null and the current node is not changed.

TreeWalker.nextNode()

Moves the current Node to the next visible node in the document order, and returns the found node. It also moves the current node to this one. If no such node exists, returns null and the current node is not changed.