DOM TreeWalker API

The TreeWalker API: A powerful tool for traversing the DOM tree.

Tom • Typescript & Javascript, Coding Guides •

The DOM TreeWalker API

The TreeWalker API allows developers to create a treeWalker object which can be used to traverse the DOM tree. The treeWalker has a number of methods which can be used to move the current position of the treeWalker within the DOM tree, as well as to return information about the current node.

The TreeWalker API is a powerful tool for traversing the DOM tree. With it, you can easily move around the tree, and get information about the nodes you encounter. The API also provides a number of convenience methods for common operations, such as getting the next or previous sibling of a node, or getting the parent node.

Example usages of the TreeWalker API

var treeWalker = document.createTreeWalker(
  document.body,
  NodeFilter.SHOW_ELEMENT,
  { acceptNode: function(node) {
      return node.tagName === 'DIV' ?
        NodeFilter.FILTER_ACCEPT :
        NodeFilter.FILTER_SKIP;
  }},
  false
);

while(treeWalker.nextNode()) {
  console.log(treeWalker.currentNode.tagName);
}

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The code above creates a TreeWalker, which is then used to traverse the DOM tree. The TreeWalker only accepts nodes which are DIV elements, and so it will skip over any other type of node. As it traverses the tree, it prints out the tag name of each DIV node it encounters. This is a useful way of finding all the DIV elements in a document.

var treeWalker = document.createTreeWalker(
  document.body,
  NodeFilter.SHOW_ELEMENT,
  { acceptNode: function(node) {
      // Check if the node is a DIV, and if it has the "my-class" class.
      return node.tagName === 'DIV' && node.classList.contains('my-class') ?
        NodeFilter.FILTER_ACCEPT :
        NodeFilter.FILTER_SKIP;
  }},
  false
);

while(treeWalker.nextNode()) {
  // Do something with the node, such as add a border.
  treeWalker.currentNode.style.border = '1px solid black';
}

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The code above does the same as the previous example, but only accepts DIV nodes which have the "my-class" class. Once it encounters such a node, it adds a 1px black border to it. This is just a simple example of what you can do with the TreeWalker API.

(Almost) all green

One of the challenges when using the TreeWalker API is that it can be easy to lose track of the current node. This is because the API does not provide any methods for finding a specific node. Instead, you have to use the methods for moving around the tree, which can be tricky. Another challenge is that the API is not very well supported by browsers, so you may have to use a polyfill.

Summary

The TreeWalker API is a powerful tool for traversing the DOM tree. It provides a number of methods for moving around the tree, as well as for getting information about the current node. The API also provides some convenience methods for common operations. However, the API can be challenging to use, and is not well supported by browsers.

Other interesting APIs related to DOM data retrieval are the following ones, which I might cover in the future.

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