Using const/let instead of var can make JavaScript code run 10× slower in Webkit

Re:Using const/let instead of var can make JavaScript code r... by lhorie on Wednesday October 21, 2020 @01:51AM (#24845110)

> the whole premise for React (the virtual DOM) is based on outdated performance advice. Chrome has used a dirty-bit

This mentality sorta falls into the exact pitfall GP mentioned (i.e. what you really want is for IE/Edge to be significantly faster bringing speed gains for everyone else along the way, not for Chrome to be microscopically faster at the expense of every other browser)

There are real and significant costs in things like random access of .childNodes or bottom-up DOM construction in some browsers. At the height of the whole virtual dom thing, there was a lot of super browser-specific micro-optimizations going on, a lot of it w/ a heavy focus on Chrome, with IRHydra and stuff.

It got a bit ridiculous when I figured out that you could make a significant dent in one of the popular benchmarks at the time not by tweaking JS anymore, but by removing unused CSS rules from bootstrap.css...

But as you said, engines change quickly and I'm not sure it's really worth to be chasing micro-optimizations anymore. We're getting to a stage where the only way to get faster is to simply run less code. Some frameworks are getting the idea (svelte, marko).

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Re:Using const/let instead of var can make JavaScript code r... by nostrademons on Wednesday October 21, 2020 @01:58AM (#24845139)

Or build better APIs into the browser and optimize them in the C++. IMHO that's the best long-term solution. Moves glacially slow, though, since there's a large engineering cost that needs the coordination of each major browser vendor.

I was a big fan of Polymer/WebComponents in 2014, but they kinda dropped the ball. In hindsight I wish they'd just implemented the React API directly in the browser. (Though depending on how Google vs. Oracle goes in the Supreme Court, maybe that'll become illegal, sigh.)

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Re:Using const/let instead of var can make JavaScript code r... by lhorie on Wednesday October 21, 2020 @02:14AM (#24845205)

This worked amazingly well for querySelector (vs jQuery's sizzle and friends at the time), but IIRC, JIT is so good now that there are APIs written in JS _because it's faster to do so than to use AOT_. I recall reading somewhere that the cost of jumping between JS and C++ land was a source of slowdowns with the DOM API, so there's that too.

But overall, I agree with the idea of incorporating the ideas that are working into the platform. There have been various discussion over the years about how virtual dom could work as a native browser API, but unfortunately, the needle hasn't moved there at all.

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Re:Using const/let instead of var can make JavaScript code r... by hardwaresofton on Wednesday October 21, 2020 @05:02AM (#24846016)

Dunno if you've looked recently but how do you feel about Polymer 3, which has essentially become lit-element (which is powered by lit-html)?

Just in case you haven't been watching the space at all:

- https://43081j.com/2018/08/future-of-polymer

- https://www.polymer-project.org/blog/2020-09-22-lit-element-...

- https://lit-element.polymer-project.org

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Re:Using const/let instead of var can make JavaScript code r... by hitekker on Thursday October 22, 2020 @11:58PM (#24865917)

I tried it for my project and found lit-html's component composition unintuitive compared to React, Svelte and other leading frameworks.

Also, I've seen the maintainer of lit-element flaming people in comment threads. It doesn't inspire confidence.

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Re:Using const/let instead of var can make JavaScript code r... by hardwaresofton on Friday October 23, 2020 @10:30PM (#24876449)

Thanks -- correct me if I'm wrong but I thought lit-element is the bit that does components and lit-html (I think the naming is pretty bad here) is just the rendering bit, is that right?

I was already on the fence about what to try next, and Svelte is at the top of the list if I have any problems with lit-element... lit-element just seems a bit lighter and more standards-positive so I wanted to give it a go.

These days though, I'm basically not considering investing in any libraries/frameworks that don't offer SSR with competent hydration. IMO it's the closest we get to the holy grail in frontend -- separation from the backend (which I argue is a benefit), and the SEO-friendliness, nojs-compatability, and speed of server side rendering.

lit-element doesn't have a good SSR story just yet (it's experimental[0]), and Svelte has sapper and ElderJS[2], so it's already ahead there...

[0]: https://github.com/PolymerLabs/lit-ssr

[1]: https://sapper.svelte.dev

[2]: https://github.com/elderjs/elderjs

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Re:Using const/let instead of var can make JavaScript code r... by spankalee on Wednesday October 21, 2020 @11:37AM (#24848860)

React would be pretty horrible to implement in the browser. It can't use most of the DOM API: you can't set properties on element, can't add event handlers to elements, create comment nodes. And VDOM and diffing is one of the slower ways to update the DOM.

We should build templating and DOM updates into the browser, but we should do better than React.

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