Skip to content
Swizec Teller - a geek with a hatswizec.com

Object clone performance: preliminary results

Spurred by debate on A Puzzle in JavaScript objects, I wanted to find the best way to clone objects in JavaScript. In this scenario, “best” means “fastest on average”.

I’m using the dataset from this visualization on H1B salaries as a quick way to build many objects. The dataset contains 81,123 objects with 9 keys each.

The experiment is set up like this:

  • load & parse data
  • run clone experiments in series
  • each experiment makes 10 deep copies of the dataset
  • “deep” is allowed to mean just the 2 levels required (objects in array don’t contain more objects)
  • present average runtime of each clone

Each individual experiment uses this runner:

runner(name, method) {
const times = d3.range(0, this.N).map(() => {
const t1 = new Date();
let copy = method(this.state.data);
const t2 = new Date();
return t2 - t1;
});
let results = this.state.results;
results.push({name: name,
avg: d3.mean(times)});
this.setState({results: results});
}

If you spot a problem with that setup, tell me.

Preliminary results, running on my laptop in Chrome 53, are a bit strange. Iterating through the array and doing Object.assign is fastest, and _.cloneDeep is slowest.

N1i7cv6

I want to add a more context-aware Lodash approach, Immutable.js, and a few different browsers. Then make some graphs :)

What’s your favorite way to clone objects in JavaScript? I’ll add it to the test.

Did you enjoy this article?

Published on September 15th, 2016 in coding, JavaScript, Technical

Learned something new?
Want to become a high value JavaScript expert?

Here's how it works 👇

Leave your email and I'll send you an Interactive Modern JavaScript Cheatsheet 📖right away. After that you'll get thoughtfully written emails every week about React, JavaScript, and your career. Lessons learned over my 20 years in the industry working with companies ranging from tiny startups to Fortune5 behemoths.

Start with an interactive cheatsheet 📖

Then get thoughtful letters 💌 on mindsets, tactics, and technical skills for your career.

"Man, love your simple writing! Yours is the only email I open from marketers and only blog that I give a fuck to read & scroll till the end. And wow always take away lessons with me. Inspiring! And very relatable. 👌"

~ Ashish Kumar

Join over 10,000 engineers just like you already improving their JS careers with my letters, workshops, courses, and talks. ✌️

Have a burning question that you think I can answer? I don't have all of the answers, but I have some! Hit me up on twitter or book a 30min ama for in-depth help.

Ready to Stop copy pasting D3 examples and create data visualizations of your own?  Learn how to build scalable dataviz components your whole team can understand with React for Data Visualization

Curious about Serverless and the modern backend? Check out Serverless Handbook, modern backend for the frontend engineer.

Ready to learn how it all fits together and build a modern webapp from scratch? Learn how to launch a webapp and make your first 💰 on the side with ServerlessReact.Dev

Want to brush up on your modern JavaScript syntax? Check out my interactive cheatsheet: es6cheatsheet.com

By the way, just in case no one has told you it yet today: I love and appreciate you for who you are ❤️