How Does React’s Interruptible Updates work? | by Zachary Lee | Apr, 2022

Why doesn’t Vue use the fiber structure?

Picture by Андрей Сизов on Unsplash

React 18 is launched, and crucial change is to help the Fiber structure. It helps React implement asynchronous, interruptible updates. This text will divulge to you the way it works.

As a result of earlier than model 17, the Diff of the digital DOM was carried out in a recursive method, and the recursive course of can’t be interrupted. It is because as soon as interrupted, it doesn’t know the place the present processing is when it begins once more.

Utilizing identification can also be a no-no as a result of operations within the DOM might be complicated and the construction of the DOM tree can change dramatically.

An uninterrupted recursive course of may cause JavaScript code to take too lengthy to execute. The browser’s rendering work and the execution of JavaScript are on the identical thread. This ends in the web page not altering in time, which makes customers really feel caught.

So the React staff adopted the Fiber structure.

React Fiber might be understood as a set of state replace mechanisms carried out inside React.

First, it may be interrupted and resumed. And after restoration, the earlier calculation outcomes and intermediate states might be reused.

Second, it additionally helps totally different priorities for updating duties. It permits these high-priority duties (comparable to consumer enter, animations, and many others.) to be rendered on the web page as early as doable.

Particular to the code, it’s a linked list-like knowledge construction. So let’s check out the definition of FiberNode within the source code:

// Occasion
this.tag = tag;
this.key = key;
this.elementType = null;
this.sort = null;
this.stateNode = null;
// Fiber
// Join with different fibers
this.return = null; = null;
this.sibling = null;
this.index = 0;
this.ref = null;// Properties of a unit of labor
this.pendingProps = pendingProps;
this.memoizedProps = null;
this.updateQueue = null;
this.memoizedState = null;
this.dependencies = null;
this.mode = mode;// Results
// Markup after Diff, used to map to the true DOM

this.flags = NoFlags;
this.subtreeFlags = NoFlags;
this.deletions = null;
// Replace schedule precedence
this.lanes = NoLanes;
this.childLanes = NoLanes;
// Present Fiber backup from final replace
// It will likely be in contrast with the present newest Fiber, which is Diff

this.alternate = null;

I’ve added further feedback and the supply code is here.

Right here I’ll deal with explaining the connection data of the Fiber node.

As proven above, they’re linked collectively in response to this linked list-like logic.

Every node is taken into account a “unit of labor”, and just one “unit of labor” is processed at a time when the browser is idle. As a result of the cut up unit of labor is sufficiently small, the JavaScript execution time is pretty brief. So this doesn’t block the browser’s rendering work.

To be extra particular, to signify this course of in pseudocode is like this:

Subsequent, let’s analyze how the Fiber node works throughout the mount part and the replace part.

The Fiber node tree on this case truly undergoes the Diff algorithm. Nevertheless, because the earlier Fiber node doesn’t exist, this Diff will mark all Fiber nodes with alternative logos.

Then within the commit part, the true DOM shall be modified in response to the identification. Right here is the addition.

A fiber node tree may even be generated throughout the replace. At the moment, the fiber node tree that has been mapped to the true DOM earlier than shall be in contrast, and the modified fiber node shall be marked.

Then within the commit part, the true DOM shall be modified in response to the identification. This could possibly be including, deleting, modifying properties, and many others.

This method is known as double caching. However why is double caching not utilized in Vue.js?

As a result of in comparison with Vue, React doesn’t know precisely which DOM (Part) an replace (State change) impacts. So it must be calculated from the start (Root) to the tip, and reuse the earlier DOM as a lot as doable throughout the calculation course of.

The recursive calculation was used earlier on this course of. Though it takes somewhat longer to execute JS, there’s nonetheless a efficiency benefit for immediately manipulating the DOM.

And now the Fiber structure is used as an alternative of recursion. The core thought is to flatten the computational price into every rendered body. On the similar time, a precedence mannequin can also be added to permit these updates with larger precedence to be rendered on the web page prematurely.

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