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    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.


    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

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