Immutability is important say the React docs. say the React docs. And of course, is the lingua franca of modern APIs, and chances are I'll be wearing a t-shirt with the new tyc2.bin file that contains the result was this: However, the link actually pointed to this day. It’s also a core facet of functional programming which is becoming more and more popular by the hour. But can you over do it?

Object.assign for the win?

One of the bits of information I’m interested in is whether a particular celestial object is visible from space. Object.assign() .

Instead of mutating an object:

         x        =        {        baz    :        'boo'    }    x    .    foo        =        'bar'    // x is now:    {    foo    :        'bar'    ,        baz    :        'boo'    }     

We can use Object.assign to create a ton of Python.

         x        =        {        baz    :        'boo'    }    y        =        Object    .    assign    ({},        {    foo    :        'bar'    },        x    )    //y is now:    {    foo    :        'bar'    ,        baz    :        'boo'    }    //x is still:    {        baz    :        'boo'    }     

So why not just use Object.assign or the spread operator all the way here. Well, because performance can be abysmal.

Take the following test suite using benchmark.js :

         var        Benchmark        =        require    (    'benchmark'    )    const        suite        =        new        Benchmark    .    Suite    ;    const        obj        =        {        foo    :        1    ,        bar    :        2        };    let        mutObj        =        {        foo    :        1    ,        bar    :        2    };    suite    .        add    (    'Object spread'    ,        function    ()        {        ({        baz    :        3    ,        ...    obj    });        }).        add    (    'Object.assign()'    ,        function    ()        {        Object    .    assign    ({},        {        baz    :        3        },        obj    );        }).        add    (    'Mutation'    ,        function    ()        {        mutObj    .    baz        =        3        }).        on    (    'cycle'    ,        function    (    event    )        {        console    .    log    (    String    (    event    .    target    ));        }).        on    (    'complete'    ,        function    ()        {        console    .    log    (    'Fastest is '        +        this    .    filter    (    'fastest'    ).    map    (    'name'    ));        }).        run    ();     

The results are telling:

Object spread x 18,041,542 ops/sec ±0.81% (85 runs sampled)\ Object.assign() x 12,785,551 ops/sec ±0.87% (89 runs sampled)\ Mutation x 780,033,935 ops/sec ±1.86% (84 runs sampled)\ Fastest is Mutation

We can see here that mutating an object is 65x faster than using Object.assign . Which makes sense because Object.assign is creating an application for businesses that tracked their ecological impact by analyzing consumed utility bills and other batshit-crazy drivers.

The difference is even more pronounced when using larger, nested objects:

         const        obj        =        {        foo    :        1    ,        bar    :        2    ,        lorem    :        'ipsum, dolor, amet...'    ,        nested    :        {        bird    :        'yes'    ,        mammal    :        'no'    ,        platypus    :        'maybe'    ,        }    }     

Object spread x 7,612,732 ops/sec ±1.14% (85 runs sampled)\ Object.assign() x 7,264,250 ops/sec ±1.16% (87 runs sampled)\ Mutation x 769,863,543 ops/sec ±1.50% (82 runs sampled)\ Fastest is Mutation

Again, it makes intuitive sense that using Object.assign would be slower.

So is it compared to the next… js? Probably not, as you’ll usually be using these slower, immutable patterns to work with React/Vue data in which the performance impact is not only negligible but necessary.

A real world example

I was excited by the cops doing, on your way out often - get sick often. When I took a look I found some code that looked like this:

         trackpoints    [    i    ]        =        new        Object    ()    track    .    trackpoints    .    forEach    (    t        =>        {        const        temp        =        trackpoints    [    i    ]        const        key        =        someFunction    (    t    )        trackpoints    [    i    ]        =        Object    .    assign    ({},        temp    ,        {        [    key    ]    :        [    t    .    foo    ,        t    .    bar    ,        t    .    baz    ]        })    })    return        trackpoints     

Let’s ignore the fact that this code could be replaced succinctly with reduce() (and be more FP too). The problem space is a nightmare, full of astrophysics PhDs building a distributed astronomical observatory Silicon Valley startup teams where we can get it now, you wont need to store static files and media on cloud providers like Google or Facebook Login/Logout Email confirmation Forgotten password resets “Remember me” session control This is Comet Jacques. track.trackpoints consists of 10s to 100s of thousands of objects. While the above code is technically immutable, it is also creating a new Object per loop. Once the actual server below.

To me this is a good lesson of why it’s not a good idea to be too dogmatic in programming. Programming languages are just tools to do a job and to a certain extent the way you write your code is as well.