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Optimize your JS code in 10 seconds

Arthur Kh on November 21, 2023

Performance is the heartbeat of any JavaScript application, wielding a profound impact on user experience and overall success. It's not just about ...
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Eckehard •

You should distinguish application performance and Javascript performance. This is NOT the same:

  • Usually, an application needs some data. Fetching data may cause a significant delay.
  • Then, Javascript can handle this data, which is usually the fastest part of the show. This is, where your "optimization" takes place!
  • After that, maybe you cause complex state changes. It may take much more time to handle all the dpendencies in your app. Luckily, all this is done on the VDOM, so it will not cause any further delay.
  • If you use React, then all your interactions have to be diffed to the real DOM
  • After the DOM is ready, the browser has to render it. This is usually the most time consuming part
  • If you change some ressources, maybe the browser needs to fetch some new images. Even that cannot be started before the DOM was ready. So, the user has to wait for all elements to be loaded.

Do you think, cutting the time of the smallest part (the Javascript routines) will cause any measureable performance boost?

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Rense Bakker •

Actually continuously updating the vdom (rerendering) is the biggest performance bottleneck for react apps (other than fetching data). The proposed optimizations help to decrease the number of rerenders as well as reduce the cost of rerendering.

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Eckehard •

If you look to the React history, the VDom was invented to free the developers from the burden of writing performant code. So, it´s really an interesting question, if streamlining your Javascript will have much impact at all. If so, React did a bad job.

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Arthur Kh •

It was invented to save time on browser DOM search and updating because DOM search methods are slower than usual JS tree/array search.
And VDOM's updating is based on the basic and fast comparison === operator instead of using deep equality, which is way slower, and it's easier to delegate reference updating to devs instead of inventing fast deep equality

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brense profile image
Rense Bakker •

VDOM was invented to make DOM updates more efficient and it did. How often you update the VDOM and how long the VDOM update takes is still up to the developer. If you loop over a million table rows on every render, obviously its going to cause problems.

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Eckehard •

You are totally right. But that means, you should avoid to loop unnecessarily over millions of table rows, not just loop faster!

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JorensM • • Edited

This gave me an idea for a library - a library that implements all the common array utils, but using the Builder pattern, so you can chain the util functions together and they will be run only once at the same time.

Anyhow great article and thanks for the tip!

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Schemetastic (Rodrigo) •

Hey! Great tips! There are other methods I like too, suchs as .trim() and .some()

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Eckehard •

It is not only a question of priority. The reasons for a delay may be very different.

If an application needs to wait for some data, we can try to use some kind of cache if the result is used more than once. Or we can change the way in which data are requested. If you need to request a database scheme via SLQ before requesting the data, you get a lot of traffic forth and back, each causing an additional delay. If you run the same operation on your database server and ask only for the result, you will get the result much faster.

But If an operation takes the same time to finish a million of loops, you would probably need a very different strategy. In that case, optimizing your code might help, but it is probably better to find a strategy that does not require so much operations at all.

To know, if an optimization helps at all, it is necessary to know, what causes the delay. Without this knowledge, you can waste a lot of time optimizing things that are fast anyway.

 
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Arthur Kh •

I completely agree that Promise.then point, async/await syntax is fantastic and widely compatible across browsers and Node environments, so it should be more prioritized.

When it comes to naming and organizing components, I'm a fan of atomic design. Its structure is exceptional, clear, and easily shareable within a team.

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Chalist •

your Telegram channel is Russian! So I can't understand, unfortunately.

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Arthur Kh • • Edited

Hey!
Image description
I've developed a bot, which automatically translates my posts to popular languages so anyone can read

It's sometimes hard to choose which language to use when you're trilingual :D

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Arthur Kh •

Thank you for your feedback, @lnahrf ! Are there any JavaScript antipatterns you're familiar with and dislike?

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Ben Sinclair •

Personally I steer clear of using reduce for all but the simplest cases because it gets unreadable pretty quickly.

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Arthur Kh •

Using .reduce might lead to unreadable code, particularly when the reducer function grows larger. However, the reducer function can be refactored into a more readable form

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Luke •

Great tips, great article, thanks!

 
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Eckehard •

See here, here, here, here, here, here, here or here.

This is from the vue-documentation:

Some applications require rich interactivity, deep session depth, and non-trivial stateful logic on the frontend. The best way to build such applications is to use an architecture where Vue not only controls the entire page, but also handles data updates and navigation without having to reload the page. This type of application is typically referred to as a Single-Page Application (SPA).

If you just have a database running on a server, I would not call this a "backend". React or Vue can run completely in the browser, so you just need a webserver and some API endpoints to get your data. An application like this would not run much faster, if you try to put the image processing on the server, but it´s worth to see, what causes the delay.

 
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Martin Ledoux •

dev.to/efpage/comment/2b22f

But things are shifting. There are a lot of SPA´s out there that just require some data and have no backend.

Realistically, they're getting the data from some backend somewhere, just not necessarily maintained by the maker of SPA. There are a lot of public APIs out there that can be consumed (which is how an SPA could have no backend but still huge data sets), and theoretically filters can be passed in requests to limit or prevent large data sets in the response.

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François-Marie de Jouvencel • • Edited

Whatever the number of loops you'll do the same exact operations !

This code:

for (let i = 0; i < 2; ++i) {
  opA();
  opB();
}
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Is almost exactly the same as

opA();
opB();
opA();
opB();
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Which again is the same as (assuming order of operations doesn't matter):

for (let i = 0; i < 2; ++i) {
  opA();
}

for (let i = 0; i < 2; ++i) {
  opB();
}
Enter fullscreen mode Exit fullscreen mode

The only thing you're saving is a counter. It's peanuts.

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Akash Kava • • Edited

Compare reduce with for of, And you would realize that for of performs faster compared to reduce.I would give least preference to reduce over for of, filter, map, reduce all can be done in a single for of.

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Arthur Kh •

The choice between using array methods like map, filter, and reduce versus explicit loops often depends on your code style. While both approaches achieve similar results, the array methods offer clearer readability: map modifies the data structure, filter removes specific elements from an array, and reduce accumulates values. However, using loops, like 'for', might require more effort to grasp since they can perform a variety of tasks, making it necessary to spend time understanding the logic within the loop's body.

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Calvin Lee Fernandes •

The code you start off with is readable but as you optimize the code, it becomes more unreadable since your fusing many operations into a single loop. Consider using a lazy collections or a streaming library which applies these loop fusion optimizations for you so you don’t have to worry about intermediate collections being generated and you can keep your focus on more readable single purpose code. Libraries like lazy.js and Effect.ts help you do this

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Ghaleb •

I don’t believe this to be accurate.

For starters, just because you're looping once doesn't mean the total number of operations changed. In your reduce function, you have two operations per iteration. In the chained methods there are two loops with one operation per iteration each.

In both cases the time complexity is O(2N) which is O(N). Which means their performance will be the same except for absolutely minor overhead from having two array methods instead of one.

Even if we assume you managed to reduce the number of operations, you can't reduce it a full order of magnitude. At best (if at all possible) you can make your optimization be O(N) while the chained version is O(xN), and for any constant x the difference will be quite minimal and only observable in extreme cases.

This is just a theoretical analysis of the proposal here. I haven't done any benchmarks, but my educated guess is that they will be in line with this logic.

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djfm profile image
François-Marie de Jouvencel • • Edited

I made a very similar comment, it pleases me to see it here already :)

I'm baffled by the number of people who seem to think that if they cram more operations into one loop they are somehow gonna reduce overall complexity in any meaningful way... But no: it'll still be O(n) where n is the length of the array.

Many people don't understand what "reduce" does, it can thus make more sense if you're in a team to use a map and a filter, which is extremely straightforward to understand and not a performance penalty.

I love obscure one-liners as much as any TypeScript geek with a love for functional programming, but I know I have to moderate myself when working within a team.

Shit, is big O complexity still studied in computer science?

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djfm profile image
François-Marie de Jouvencel • • Edited

While doing more operations in one loop is gonna save you incrementing a counter multiple times, you'll still have O(n) complexity where n is the size of your array, so you will most likely not save any measurable amount of resources at all.

Sometimes it is more clear to write map then filter just for readability, cuz not everyone understands what reduce does unfortunately.

Code that cannot be read fluently by the whole team is in my experience way more costly than a few sub-optimal parts in an algorithm that takes nanoseconds to complete.

You should study the subject of algorithmic complexity if you don't know much about this concept.

 
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Eckehard •

But things are shifting. There are a lot of SPA´s out there that just require some data and have no backend.

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