Memoize Context

[00:00] Alright, we've got our memoized footer, we have our use footer, we have our footer context, all of this. And the problem is that our footer context value is changing every render because we're creating a brand new object every time. So triple equals false.

[00:14] We need to make it so that these, this object will only be a different object if the properties of it are different. So we're going to add use memo from react here. And that will wrap this guy.

[00:29] And we'll let the ESLint plugin throw those values in there, save that. And then if we clear this out and record and increment the app count, then we should not see the footer re-render in here because the context value itself didn't change. So this value remained the same.

[00:48] Of course, you do want to make sure that it is still able to perform the stuff that it's supposed to do. But yeah, that seems to be working just fine.

[00:00] So now our example has this idea of a footer context that accepts both the color and the name. So both of these elements of state are in the context provider, and the footer will consume that. And the optimization that we want to make now is if you change the state for the app count,

[00:18] that shouldn't re-render the footer because the footer doesn't care about the app count. It only cares about the color and the name. But what we're observing is not that. We are observing that when you increment the app count, the footer is going to re-render unnecessarily. So let's check that out.

[00:37] Increment the app count and turn that off. And we will see that the footer is indeed getting re-rendered. We have source maps and some weird things, so this is called footer 2. This is our memoized footer component.

[00:51] So that is re-rendering because the context changed, even though the individual values of context did not change. So we need to memoize this. I want you to first, before you start, pull this up and run that. Make sure you're seeing the same thing.

[01:05] And then go ahead and implement the use memo around this thing and check it again. Like most of the performance optimizations, we're doing not a lot of code changes, but I want you to be spending time in the DevTools here anyway. So see you when you're done.

In this workshop you will diagnose, profile, and fix performance problems in your React application using the Browser Profiler, React DevTools Profiler, and optimization techniques.

There are always trade-offs to consider when thinking about optimization. 

You will be learning optimizaiton patterns in this workshop. 

But, more importantly you'll be learning how to measure the performance of your app, carefully consider the complexity trade-offs of optimization, and understand which optimizations apply to certain situations. 

By the end of this workshop you'll understand how to: 

- Prevent unnecessary re-renders
- Render concurrently
- Lazy and eager load components
- Use memoization and web workers
- and use windowing with react-virtual


## Element Optimization

Gain practical experience optimizing React component rendering. 

Learn to hoist React elements to prevent unnecessary renders, pass elements as props, use React's Context API to trigger re-renders only on necessary state changes, and apply useMemo and React.memo.

## Optimize Context 

Here you'll learn three ways to optimize context: Memoize context values, create a provider component, and split context values into setter functions. 

In addition to the techniques, this will teach you how to use the devtools to determine which ones you need to use. 

## Concurrent Rendering

Sometimes, you're rendering so many components or those components are doing such complex things that you can't afford to render them all quickly enough.

Find out how to use the useDeferredValue hook and memo to prioritize the rendering of some parts of your app over others.

## Code Splitting

Code splitting acts on the principle that loading less code will speed up your app. There are three ways we'll approach it in this section:

Lazy loading, eager loading, and transitions. 

In lazy loading you'll learn how to use React's lazy method for lazy loading components

Eager loading is like a layer on top of lazy loading. You'll learn how to deferr the loading of a component until some event occurs like a mouse over or on focus. 

In transitions you'll learn to optimize the loading experience using the useTransition hook and the useSpinDelay hook from the spin-delay package.

## Expensive Calculations

JavaScript is single-threaded which poses a problem when you need to deal with some kind of expensive calculation. 

React has ways of dealing with this but if you are outside of React-land you'll be blocking the thread while the calculation is being performed. Luckily there are a couple options for dealing with this.

**useMemo** is useful if you're working with indempotent functions. And if you aren't, **Web Workers** let you perform the calculations on a separate thread but they add some complexity  to your code.

Throughout this workshop you'll be learning to measure performance and weigh the trade-offs of all the techniques you learn!

## Optimize Rendering

React is pretty smart about determining when it needs to re-render. But, sometimes there are cases we can get a bit of an edge over it ourselves. 

If your components are re-rendering when a DOM update isn't actually needed, you'll want to reach for memo and memoize your components. 

But, what if memo's built-in comparitor isn't doing the trick? It works off a simple Object.is. Which is great most of the time but if you're dealing with complex props you have the option of passing a custom comparitor function. 

## Windowing

And lastly you'll be exploring an advanced technique for when you're dealing with a truly massive amount of elements. 

There's only so much optimizing you can do when you need to rendering thousands of elements. But, what if you only had to render a slice of them? That's where windowing comes in. 

You'll be using the @tanstack/react-virtual library to virtualize only the visible DOM nodes (and a few nodes outside of view for the fast-scrollers) in a large scrollable element.

Diagnose, profile, and fix performance problems in your React application using the Browser Profiler, React DevTools Profiler, and optimization techniques.

React Performance

React Performance

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Memoize Context

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