MutationRecord: previousSibling 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 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/removes a node every time you click the button. Then the observer logs the textContent of the previousSibling of the updated node.
HTML
<button id="add-nodes">Add a node</button>
<button id="remove-nodes">Remove a node</button>
<button id="reset">Reset</button>
<pre id="log" class="log">Previous sibling of updated node:</pre>
<div id="target"><p>Node #0</p></div>
JavaScript
const addNodes = document.querySelector("#add-nodes");
const removeNodes = document.querySelector("#remove-nodes");
const reset = document.querySelector("#reset");
const target = document.querySelector("#target");
addNodes.addEventListener("click", () => {
const newPara = document.createElement("p");
newPara.textContent = `Node #${target.childElementCount}`;
target.appendChild(newPara);
});
removeNodes.addEventListener("click", () => {
const oldPara = target.lastChild;
if (oldPara) {
target.removeChild(oldPara);
}
});
reset.addEventListener("click", () => self.location.reload());
function logPreviousSibling(records) {
for (const record of records) {
if (record.type === "childList") {
log.textContent = `Previous sibling of updated node: ${record.previousSibling?.textContent ?? null}`;
}
}
}
const observer = new MutationObserver(logPreviousSibling);
observer.observe(target, { childList: true });
Result
Specifications
| Specification |
|---|
| DOM # ref-for-dom-mutationrecord-previoussibling② |