Part 8

8.0 Part 8 (clickable)


We know how mounting works, but now, let’s go from the another side. Yes, setState method, one more piece of cake!

First of all, why we actually can call some method called setState? Well, that’s clear enough, we inherited our component from ReactComponent. Alright, then, it’s easy to find this class in React source and check its setState method.

this.updater.enqueueSetState(this, partialState)

As you can see, there is some updater interface. What that updater is? Well, if you check mounting process we’ve just analyzed, during mountComponent, instance receives updater property as a reference to ReactUpdateQueue (src\renderers\shared\stack\reconciler\ReactUpdateQueue.js).

Well, dive inside enqueueSetState (1) method and see that, at first, it pushes partial state (a partial state is an object you pass into this.setState) to _pendingStateQueue (2) of internal instance (just to remind: public instance, it’s actually our custom component ExampleApplication and, internal instance is ReactCompositeComponent which was created during mounting), secondary, we enqueueUpdate, what actually check if updates already in progress and push our component to dirtyComponents list, otherwise, if not - init update transaction and then push component to dirtyComponents list.

To summarize this, each component has own list of pending states, means, each time you call setState in one transaction, you just push that objects into a queue, then, later, they will be merged into component state one by one. And, when you call setState, you add your component into dirtyComponents list. Probably, you are already wondering, how that dirtyComponents are processed? You are right, that’s next important piece of the puzzle…

Alright, we’ve finished Part 8.

Let’s recap how we got here. Let’s look at the scheme one more time, then remove redundant less important pieces, and it becomes this:

8.1 Part 8 simplified (clickable)

And we should probably fix spaces and alignment as well:

8.2 Part 8 simplified & refactored (clickable)

Nice. In fact, that’s all that happens here. So, we can take the essential value from Part 8 and use it for the final updating scheme:

8.3 Part 8 essential value (clickable)

And then we’re done!

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