Virtual DOM: Back in Block

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The virtual DOM is generally regarded as a necessary evil, a performance tax that we have to pay for the convenience of declarative UIs.Until now.In this talk, we'll take a deep dive into what the block virtual DOM is (an new, innovative approach to VDOM), and how Million.js can help you improve the speed of your React applications. This talk will also provide a helpful overview of how the React virtual DOM works. By the end of this talk, you'll have the knowledge to not only start improving your React apps' performance with Million.js, but understand the underlying internals that make it so fast.

Aiden Bai
Aiden Bai
9 min
15 Nov, 2023

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Video Summary and Transcription

Hi, I'm Annembae, the author of MillionJS, a fast virtual DOM replacement for React. The virtual DOM can be slow depending on the components it powers. The block virtual DOM introduces an O(1) optimization to the traditional virtual DOM, resulting in faster updates with fewer DOM manipulations. MillionJS and the Block Virtual DOM offer a faster alternative to existing virtual-dom libraries like React. It has the potential to revolutionize the way we write React applications.

Available in Español: DOM Virtual: De vuelta en Bloque

1. Introduction to Virtual DOM

Short description:

Hi, I'm Annembae, the author of MillionJS, a fast virtual DOM replacement for React. The virtual DOM has been criticized as pure overhead, but now it's time to reconsider. The virtual DOM can be slow depending on the components it powers. It works by representing the user interface as a tree and updating it with a diff algorithm.

Hi, my name is Annembae. I'm the author and creator of MillionJS, a fast virtual DOM replacement for React. I'm also a student at the University of Washington for CS. Actually, this is my dorm right here. So today I'll be talking to you guys about virtual DOM, but this time, back in block.

A little over four years ago, Rich Harris released Virtual DOM is Pure Overhead. Rich most notably said, you've probably heard the phrase, the virtual DOM is fast, often meant to say that it's faster than the real DOM. In fact, it's a surprisingly resilient meme. In this article, Rich Harris argues that the virtual DOM, a widely praised feature of frameworks like React, is not as efficient as many of us believe. He goes on to critique the way it works and presents Svelte. But what followed years after was the emergence of a new meme, that the virtual DOM is pure overhead. The meme became so resilient that it turned the no virtual DOM framework movement from an iconoclastic subgroup to a fully fledged crusade. Thus, the virtual DOM was relegated to the annoying cousin nobody likes but has to invite to family gathering status. It became a necessary evil, a performance tax that we had to pay for the convenience of declarative UIs. Until now.

So the natural question everyone or you guys are probably asking is why is the virtual DOM slow? But I think a better question to ask is when can the virtual DOM be slow? And it's all because of this guy. You've probably heard of his music video. I don't actually mean this guy, but rather the component that powers him. Let's take a look. One branch is a code return unless you're AngularJS. If math.random is over .5. It can also return, you know, the rick rule gif. So you can see here naturally that there could be an update between the rick rule and the AngularJS. So how does this work? Well, there, here's where the virtual DOM comes in. So the virtual DOM is essentially a tree or data representation of the user interface, or in this case the DOM. You can see here that there are five nodes in the old virtual DOM tree, and there's three nodes in the new one. So how do we update the user interface based on these trees? Well, we run a dif. So we traverse both trees at once. First, we check the first node. Has the first node changed? I don't think so.

2. Introduction to Virtual DOM Optimization

Short description:

How about the second one? Two has been changed to five. We can do a DOM update. If we check the third one, the third node has been removed. The virtual DOM is really nice because it can process all nodes and do the minimum amount of DOM updates. But when you have more nodes, it becomes inefficient. So today I'm going to introduce a new approach to doing the virtual DOM by diffing the data instead of the DOM.

How about the second one? Yes. Two has been changed to five. And so what we can do here is do a DOM update. It's just like doing dot intertext or replacing a node or whatever.

Let's go on. If we check the third one, we can see that the third node has been removed. And so we can remove it in the DOM. So on and so forth. You can see here that the virtual DOM is really nice because it doesn't matter what the shape of their UI looks like. It doesn't matter how much nodes we have. Eventually we can process all of them and do the minimum amount of DOM updates to the page. So this is great, right? Essentially, you can change old UIs to new UIs using this virtual tree structure.

But what happens when you have more nodes? Uh oh, you're doing five diffs. It's nice when you have five diffs because you're going to have to change five nodes anyway. But what happens when you only change one node? Well, you still have to do five diffs here, right? You have to check if foo is the same. And in this case, you only update one. So this can get really inefficient. So imagine it as O of n. As your UI gets bigger, the more you have the diff, the slower your app gets. And here's a visualization of that. Once you have 200 nodes in your page, it gets really slow.

So today I'm going to introduce something new. A new approach to doing the virtual DOM. Instead of diffing the tree structures and doing all this stuff, what if we just diff the data and not the DOM? Well this all starts with a compiler. The compiler can look at the virtual DOM ahead of time. So we still have this tree structure here, it's just not in the runtime. So here we know the relationship between the data and the UI here. So you can imagine in React, you have a use state with a count or whatever. This could be a count or this could be a node in our case. We don't necessarily know the values beforehand, so we put a placeholder node inside of these.

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