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Because it can be automated? Every app that doesn't do this is just implementing the diff by hand, e.g. on this event delete this element, update this element,

Because it can be automated? Every app that doesn't do this is just implementing the diff by hand, e.g. on this event delete this element, update this element, add CSS class to this element, etc. When the UI gets complicated you have to maintain this all yourself and it's a pain. Multiple event listeners between components to say something has happened. It makes sense to be able to describe what you want to achieve and to let the browser determine how to get there in the most efficient way. If the browser could do this it would make a tonne of JS code so much simpler. There's a lot that goes into making sure that there's no unnecessary DOM updates because it's just slow. I don't write assembly and move things between registers by hand, I write a function and the compiler decides the most efficient way of doing it. UI should be the same way, I say what I want to happen and the browser decides how to get there.

5560675260 4y ago
> When the UI gets complicated you have to maintain this all yourself and it's a pain This is also something that can be automated by a framework. Check out https://svelte.dev/blog/virtual-dom-is-pure-overhead https://svelte.dev/blog/virtual-dom-is-pure-overhead
- Philip-J-Fry 4y ago
  Yes... but that's the exact argument I'm making here. Unless you want to go through that pain, you need a framework. Whether that's Svelte without a VDOM or React with a VDOM. The entire point of these frameworks is that you can write complex UI in a declarative way. They both exist because writing it declaratively in pure JS leads to performance issues. But there's nothing stopping the browser implementing something that does this optimisation for you.
  - recursive 4y ago
    I find the "pain" to be drastically overstated. See this HN post.
    - noahtallen 4y ago
      I mean, it’s clear that with a single view, it’s possible to manage this without too much trouble. But next to no apps are single views. And any project that has multiple people working on it is going to have multiple views and features which all interact in interesting ways. It’s definitely not overstated. Try writing a moderately involved app yourself in plain JS! It does get to be a pain, I’ve done it! By the time you finish, you’ll have likely created some level of abstractions, and invented yourself a nice new JS framework for yourself ;)
bobbylarrybobby 4y ago
Yes, but there are ways to accomplish this automation without diffing. Svelte does this by statically wiring up the data dependencies in your app when it builds, and then at runtime making exactly the changes to the DOM that it needs to based on the information it had at build time. No need to diff.
- Philip-J-Fry 4y ago
  The point is that A) that's a framework and B) that requires you to compile Svelte files. If you want to write declarative UI in pure JS then you need the browser to do these DOM optimisations for you, and diffing the changes is the way to do that.

5560675260 4y ago

> When the UI gets complicated you have to maintain this all yourself and it's a pain This is also something that can be automated by a framework. Check out https://svelte.dev/blog/virtual-dom-is-pure-overhead https://svelte.dev/blog/virtual-dom-is-pure-overhead

Philip-J-Fry 4y ago
Yes... but that's the exact argument I'm making here. Unless you want to go through that pain, you need a framework. Whether that's Svelte without a VDOM or React with a VDOM. The entire point of these frameworks is that you can write complex UI in a declarative way. They both exist because writing it declaratively in pure JS leads to performance issues. But there's nothing stopping the browser implementing something that does this optimisation for you.
- recursive 4y ago
  I find the "pain" to be drastically overstated. See this HN post.
  - noahtallen 4y ago
    I mean, it’s clear that with a single view, it’s possible to manage this without too much trouble. But next to no apps are single views. And any project that has multiple people working on it is going to have multiple views and features which all interact in interesting ways. It’s definitely not overstated. Try writing a moderately involved app yourself in plain JS! It does get to be a pain, I’ve done it! By the time you finish, you’ll have likely created some level of abstractions, and invented yourself a nice new JS framework for yourself ;)

bobbylarrybobby 4y ago

Yes, but there are ways to accomplish this automation without diffing. Svelte does this by statically wiring up the data dependencies in your app when it builds, and then at runtime making exactly the changes to the DOM that it needs to based on the information it had at build time. No need to diff.

Philip-J-Fry 4y ago
The point is that A) that's a framework and B) that requires you to compile Svelte files. If you want to write declarative UI in pure JS then you need the browser to do these DOM optimisations for you, and diffing the changes is the way to do that.