Performance of MutationObserver to detect nodes in entire DOM

javascript

performance

mutation-observer

dom

byNikita Barsukov·Sep 18, 2024

Boost MutationObserver efficiency by narrowing its watch area to a specific element and tailoring mutation checks. Put it to work like this:

// Grab the element like it's the last piece of cake
const myElement = document.getElementById('myUniqueJohnDoeElementID');

// Set your observer to look for specific changes
const config = { childList: true, subtree: true };

// You handle only the mutations that matter here
const efficientCallback = (mutations) => {
  mutations.forEach(mutation => {
    if (mutation.addedNodes.length) {
      // Do something cool with your new nodes here
    }
  });
};

// Tie your observer to specific element with your defined configuration
new MutationObserver(efficientCallback).observe(myElement, config);

Use this template as it focuses on specific mutations avoiding unnecessary overhead, ensuring your app remains smooth and responsive.

Fit the .observe() method's attributeFilter option to your requirements to ensure lean performance:

const config = {
  attributes: true,
  attributeFilter: ['data-value', 'title']
};

Now only changes to the selected attributes will result in your callback being invoked, preventing unnecessary operations.

Avoid accidental layout recalculations

Cautiously avoid accessing layout-triggering properties like offsetTop to prevent forced synchronous layouts that may hinder performance.

Prefer nonrecursive observation when possible

A smart move to lighten the observer's burden, is to set the subtree option to false. This nonrecursive strategy hones the observer's view to directly parent nodes, not the entire substructure.

Direct element access for speed

When possible, hitch a getElementById or querySelector to locate elements directly instead of trawling through the potentially long mutation list:

if (mutation.addedNodes.length) {
  // Why walk when you can teleport directly?
  const newNode = document.getElementById('freshNodeID');
}

Managing heavy processing

When confronted with bulky operations, lean on debounce to maintain a responsive UI whilst managing heavy processing. It's like having your cake and eating it too.

Identifying observer bottlenecks

Leverage the Chrome DevTools profiler to scrutinize your callback function. Discover the weakest points and strengthen your JavaScript muscles.

Deferred observation schedule

For non-critical observations, you might want to temporarily disconnect the observer and plan a recon at a later time:

const missionControl = new MutationObserver(mutationCallback);
missionControl.disconnect();

// Give it a coffee break
setTimeout(() => {
  // Kick back into action when it's crunch time
  missionControl.observe(target, config);
}, 0);

This technique saves processing power when observing changes to off-screen elements.

Efficient handling with libraries

Consider using a speedy library, such as lodash, for complex list handling, it's the Ferrari to native methods' go-kart when it comes to large data sets.

Picking your battles with query selectors

querySelector and querySelectorAll are potent tools, but yielding them carelessly may lead to perf drops, so opt for their use in high-value scenarios only.

Visualization

Think of the DOM as those trendy, modern condominiums, and nodes as individual condos:

🏙️ DOM Condos - Number of units for sale: Nodes

The MutationObserver is like a super-efficient real estate agent (💼):

🕴️ DOM Realty: monitoring vacancies and purchases...

Their objective is to keep an efficient track of sales, just like an agent maximizes their commissions:

Performance mantra: Close sales on important units, avoid the window-shopping crowd!

Efficient sales agent:

🕴️ Focused Agent: [New Loft 🏢, Renovated Condo 🛠️, Foreclosed Unit 💥]

Inefficient sales agent:

🕴️ Scatterbrained Agent: Trying to sell every pebble and blade of grass on property🧱🔍- Low closing rate! (Avoid these agents ❌)

Deciding between quick closings & total client coverage unlocks the key to real DOM realty success. 🏙️✨

Key takeaways

You should now be well-equipped to optimize your MutationObserver usages, saving cycles and ensuring better performance, because don't forget, the best code is the code that runs the fastest.

explain-codes / Javascript / Performance of MutationObserver to detect nodes in entire DOM

Linked

How to wait until an element exists?



How to add/update an attribute to an HTML element using JavaScript?



How to auto-scroll to end of div when data is added?



Check with jquery if div has overflowing elements



Remove all child elements of a DOM node in JavaScript

