MutationRecord: previousSibling property

The MutationRecord read-only property previousSibling is the previous sibling of an added or removed child node of the target of a MutationObserver.

Value

If a node is added to or removed from the target of a MutationObserver, the value is the Node that is the previous sibling of the added or removed node: that is, the node immediately before this one in the parent's childNodes list.

The value is null if there are no added or removed nodes, or if the node is the first child of its parent.

Examples

Log the previous sibling of a mutation

This adds a node every time you click the button. Then the observer logs the textContent of the previousSibling of the added node.

HTML

html

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

<pre id="log" class="log">Previous sibling of added node:</pre>
<div id="target"><p>Node #0</p></div>

.log {
  border: 1px dotted black;
  padding: 0.5rem;
}

JavaScript

const addNodes = document.querySelector("#add-nodes");
const reset = document.querySelector("#reset");
const target = document.querySelector("#target");
let nodeNumber = 1;

addNodes.addEventListener("click", () => {
  const newPara = document.createElement("p");
  newPara.textContent = `Node #${nodeNumber}`;
  nodeNumber++;
  target.appendChild(newPara);
});

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

function logPreviousSibling(records) {
  for (const record of records) {
    if (record.type === "childList") {
      for (const newNode of record.addedNodes) {
        log.textContent = `Previous sibling of added node: ${newNode.previousSibling?.textContent}`;
      }
    }
  }
}

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

Result

Specifications

Specification
DOM Standard # ref-for-dom-mutationrecord-previoussibling②

Browser compatibility

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