MutationRecord: addedNodes property

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 MutationRecord read-only property addedNodes is a NodeList of nodes added to a target node by a mutation observed with a MutationObserver.

Value

A NodeList containing the nodes added to the target of the mutation observed by the MutationObserver.

In the following example, there are two buttons: one to add new nodes to a target node, and one to remove them. A MutationObserver is used to observe the target node for changes; when a change is detected, the observer calls a function, logNewNodes().

The logNewNodes() function checks that the MutationRecord's type is childList, which means that the target node's children have changed. If the type is childlist the function updates the total number of new nodes that have been added. However, note that clicking the "Remove a node" button will not increment the total number of new nodes, because in this case record.addedNodes will have a length of 0.

HTML

html

<button id="add-nodes">Add a node</button>
<button id="remove-nodes">Remove a node</button>
<button id="reset">Reset</button>

<pre id="counter">Total added nodes: 0</pre>
<div id="target"></div>

#counter {
  border: 1px dotted black;
  padding: 0.5rem;
}

JavaScript

const addNodes = document.querySelector("#add-nodes");
const removeNodes = document.querySelector("#remove-nodes");
const reset = document.querySelector("#reset");
const counter = document.querySelector("#counter");
const target = document.querySelector("#target");
let totalAddedNodes = 0;

addNodes.addEventListener("click", () => {
  const newPara = document.createElement("p");
  newPara.textContent = `Current time: ${Date.now()}`;
  target.appendChild(newPara);
});

removeNodes.addEventListener("click", () => {
  const lastChild = target.lastChild;
  if (lastChild) {
    target.removeChild(lastChild);
  }
});

reset.addEventListener("click", () => self.location.reload());

function logNewNodes(records) {
  for (const record of records) {
    // Check if the childlist of the target node has been mutated
    if (record.type === "childList") {
      totalAddedNodes += record.addedNodes.length;
      // Log the number of nodes added
      counter.textContent = `Total added nodes: ${totalAddedNodes}`;
    }
  }
}

const observer = new MutationObserver(logNewNodes);
observer.observe(target, { childList: true });