Hey everyone! I just launched 🚀 Project React, which is a course that teaches you React by building a real-world project. It goes way beyond what you see in these videos and walks you through step-by-step on how to build a big and complex application with React! You can check it out here: cosden.solutions/project-react

@EnesKab

Ай бұрын

Please add also NextJS to the Project React Course 🙂

After watching 3 of your videos I have learned more than reading 3 books on React. Your videos are exceptionally clear. Thanks

This was my first and the last useMemo tutorial. I just loved the way you isolated the concept along with a really simple explanation. Thank you!

Thank you for explaining these concepts so simply! Love your videos.

I am so happy that I got landed to this channel. So concise, loving it.

The best useMemo explanation I've seen.

This could be the best useMemo tutorial I've seen. And I've seen a lot. Almost too many. 😂 Oh, and I love that you keep rounding 29.999.999 to 29 million. Made me chuckle every time... 🤗🤗

I've been struggling with this concept, but this video really made it easy and simple to understand. Many thanks!

@cosdensolutions

11 ай бұрын

glad it helped! 🤙

thank god i stumbled upon your channel..i am learning about all the hooks that react has to offer through your channel..i am loving the clear explanations that you provide..not a single dull moment in the video! kudos to you sir! love you!!!

It's definitely the best explanation I've ever seen. Thank you very much!

Done thanks clear 6:50 useMemo memoizes the result of a calculation/ function call until some dependencies change

As someone still new to react and web dev in general, this is awesome, the main hooks I’ve been using have been useState and useEffect. Would be great to see one about useRef too :)

@cosdensolutions

Жыл бұрын

It's coming! Just started this 😁

Thank you very much for the easier explained concepts. I'm watching your videos to understand my lessons better. Both compliment each other well.

@cosdensolutions

8 ай бұрын

wonderful!

You have the best tutorials channel 🙌🙌🙌🙌

Wow... perfectly explained man, Thanks.

So simply explained! wow, amazing

Timing the "like and subscribe" popup exactly after you explain the solution is genius. I clicked like and it felt good I don't know why lol

Love your explanations, you have made react a lot simpler.

Really useful tutorial. Thanks for being so helpful!

Simply explained indeed, Thank you.

you are THE BEST to explain!

Best explanation ever. understand in one go.

the best video explains useMemo!! thank you so much!

So good! You explained it perfectly!

this was a perfect explanation - thank you!

Made me rethink the way I was seeing this hook. Thanks

that was very helpful, thank you for clearing the confusion

Thank you for your clear explanation ❤

the most clear explanation!

Great video, thanks for this, I'll have to look at implementing this now.

This guy is the best teaching react stuff

Wonderful !! 👏 I subscribe right away !

I like your tutorial very short and will explain. Thank you so much 😊😊

No one has ever articulated this topic so well. Because it's simple yet confusing. Also I was tired of watching premium full blown course about shopping cart app with tailwind and what not, all to explain the few key concepts hardly for 5 mins which eventually gets buried somewhere in the middle. Thanks for the short and sweet content.

Great explanation, thank you!

Great explanation!

awesome explanation, thanks

Best tutorial for useMemo!

This video helped me a lot.

Well explained Thank you very much.

Once again great tutorial...

Great explication bro. Thank you very much

Awesome...very well explained

great explanation, thank you very much!

Very well explained!

Thank you, great explanation

Hey, i really like your way of explaining. I bought an online course on React, but sometimes I just don't get it on the course, and your videos make it super duper clear for me. Thank you for your job, wish you all the best, and I hope some day you are going to have 500k subs on youtube.

@cosdensolutions

8 ай бұрын

thank you for the kind words! I'm also working on a course by the way, will have this teaching style and a really well thought out plan that I haven't seen done in another course before! Coming in a couple of months

Great video I just begin my react js journey and can easily understand the concept

Ohhh mannn. Why are you so good at teaching? Thank you so much!!!

@cosdensolutions

9 ай бұрын

You're most welcome ☺️

thanks alot , very helpful🌹

Ohh man nicely explained 🎉❤

that is the perfect fundamentals . it was very efficient to understand the how important useMemo . thx :)

@cosdensolutions

11 ай бұрын

Glad you found it useful! 🤙

Appreciate your explanation ! thanx

Good stuff, thanks

Hi, your way of teaching is very easy to understand and helps me learn more concepts. Please make a video on Reactjs Forms as well.. it would really help me understand forms better. Thanks for making learning so easy and effective.

Great one!! thanks bro

Thanks for this video 👍👍👍 really good way that you explain . I am lazy person who understand only if simplify way to explain of context and you did it 😜🤗. Good job..!😊

Im enrolled in a couple of intermediate and advanced react courses.. even bought a couple of books.. But man, your vids are waaay better and so amazing! clear and concise!!!! i wish you had a full on intermediate/advanced react course. i would gladly pay for that! Thank you so much for existing!!!

@cosdensolutions

3 ай бұрын

I'm just about to launch a course that has 2 parts. The first part is more beginner, the second is more intermediate/advanced ☺️ if you get it when it launches you get both for the price of one

@SWE507

3 ай бұрын

Will be sure to do so!! thank you! :D @@cosdensolutions

Amazing amazing amazing explanation bro . ♥️♥️♥️♥️♥️. Plss do a javascript series also

Really its a Last Usememo video for me🥰🥰🥰

Best video ever❤❤

Thanks, man

best teaching

Well explained

dude you're awesome. Thank you so much for your explanations, now I guess I don't need to watch other videos about react hooks :)

@cosdensolutions

7 ай бұрын

☺️

Thanks man

thank you so much

Really well explained, thank you. Also mind dropping a list of most common cases that you would use useMemo for?

@cosdensolutions

9 ай бұрын

I would only use it when there's an expensive computation to make, or when I want to prevent this from causing a expensive child component to re-render

God tier video

Thank you

every tutorial of cosden solution is last tutorial ur gonna watch - Fr ✌✌

Thanks, Alot Man. Glad i picked your video first now i don't need to watch another video on this.

@cosdensolutions

10 ай бұрын

🤙

Nice explanation, appreciate that. Btw dude how do you spam that fast!

Thanks a lot!

Hi sir, I am grateful that I landed here and learn some valuable concepts of useMemo, I have a question that on 11:30 minute you added the count as a dependency array, now when a count changes that computation will run again, then how the usememo is beneficial here, let me know please?

@cosdensolutions

7 ай бұрын

The useMemo is not to prevent a re-render, but rather control when it happens. In that example we did indeed invalidate what we did by adding count, however that's necessary. Our memo depended on count so we had to provide it. The benefit lies when we add a new state variable that is not related to that, then useMemo won't re-render when that changes. So again, we're not trying to prevent a re-render, but rather control when it happens and only have it happen when absolutely necessary, otherwise return the memoed value

all your video is awesome keep it up ,make small project which make use of the all hooks how to use in company level or share some difficult situation of it when to use which hooks use it will be great help

@cosdensolutions

6 ай бұрын

Currently in the process of making a full on course with exactly that!

Love it the way you explained everything single detail, Can I also use useMemo with autocomplete with fetch?

@cosdensolutions

3 ай бұрын

yeah you can!

Ty bro

Would be great if you push the code at the start of the video to a different branch and the end product to the master branch so we could code along

Great

Awesome explanation, thank you. Could you provide the name of the theme you are using too?

@cosdensolutions

Жыл бұрын

Material theme darker! 🤙

so useMemo is fairly similar to useEffect? but useEffect is called when the page is loaded and/or for some dependencies?

Hi, I’m new to react and your videos are really helpful. I have two questions: 1. In the last specific scenario, is it really necessary using useMemo? I mean, the only cause of rerender is when count changes, so useMemo would compare every render the dependecies. 2. What is the differences between useMemo and useCallback?

@cosdensolutions

8 ай бұрын

1. In the context of the video, no it isn't. But the goal was to show you how it works! 2. useMemo returns a value, useCallback returns a function. They are the same otherwise!

@dariotizzoni1517

8 ай бұрын

Oh, that’s right! Really thanks 😊

Great videos. 1 question though, when you have count and items in the hook, why doesn't that lag as it seems like the items are being looped each time count changes?

I reviewed some custom hooks and sometimes found useCallback/useMemo with an empty dependency array. Could you explain why that is?

Great Explanation, thank you. I have 1 doubt. If I use useState to store the value of selected items and changed its value only when there is change in the dependency array of the useEffect hook, then will it produce the same result? If yes then what is the difference between the two ? function Demo({}: DemoProps) { const [count, setCount] = useState(0); const [selectedItem, setSelectedItem] = useState(0); const [items] = useState(initialItems); useEffect(() => { const temp = items.find((item) => item.id === count) setSelectedItem(temp) }, [items]) return ( Count: {count} Selected Item: {selectedItem?.id} setCount(count + 1)}> Increment ); }

@cosdensolutions

11 ай бұрын

So first of all in your example you're missing `count` in your dependency array. You want that useEffect to run as count changes, as well as when items changes. Second of all, that code is equivalent, but now you have an extra piece of state + the hook that keeps it in sync. The way I showed in the video is better because the "sync" happens automatically. That approach is better because it has less code (one less hook) and less responsibility (selectedItem is auto updated through `useMemo` without manually having to do anything) So you're basically doing the same work, just with extra dependencies, which isn't ideal 😁 best to keep things simple and automatic

@sweekiatwong8995

9 ай бұрын

was thinking the same thing glad to have found this exchange in the comments

@bbbeo8912

5 ай бұрын

Thank you both for asking and answer. I'm about to ask the same but got the point here.

Hey cosden, we can achieve the similar results using useEffect ? so how do we identify when should we use memo ? // Use effect equivalent: import { useState, useMemo, useEffect } from "react"; import { data } from "./utils/data"; const Counter = () => { const [arr] = useState(data); const [selectedValue, setSelectedValue] = useState(0); useEffect(() => { const val = arr.find((elem) => elem.isSelected); setSelectedValue(val); }, [arr]); const [count, setCount] = useState(0); return ( Count:{count} setCount(count + 1)}>+1 selectedValue : {selectedValue.id} ); }; export default Counter; Thnaks for the video. Can you make a complete project in react with best practices. Thanks.

@cosdensolutions

4 ай бұрын

So while your example works, it's not the recommended approach. The way you have it, you have an extra state variable that you have to manage and a whole useEffect to manage it. If you do it like I showed in useMemo, then selectedValue automatically gets re-computed when the array changes, and you don't have to do it yourself. That's why it's a better approach. There are a lot of times where something shouldn't be done with an useEffect even if it can, just because it introduces an extra dependency you have to manage and keep up to date. Also, your example creates an extra render cycle in the component which is unnecessary

This hooks series are great!! I had a question.Is there a way to gauge when to use useMemo vs not? In our case it made sense simply because of the sample size of array being over 29million but realistically it's hard to determine this intuitively...or even with our simply array at what size would be the cut off(to use/not use useMemo). I guess this question is applicable to useCallback too.

@cosdensolutions

8 ай бұрын

the general idea is to do it whenever you're mapping over something or computing something expensive. If you have that, you generally want to wrap that in useMemo so that it doesn't unnecessarily run every time. The more you work with it, the more experience you have and you learn to intuitively know when and when not to use it

I really like your videos - they are very informative and educational. I have only one question - what if we know that items won`t change (e.g. these are the static backend property). Could we define the selectedItem outside the component and then use it. e.g.: import { initialItems } from './utils'; const selectedItem = initialItems.find(item => item.isSelected); functionDemo({}: DemoProps){ //Rest of code without any of useState and useMemo hooks for items } It will work and the find will run only once, (when refreshing the website and rendering the full component); I know that it would be working only in edge case when we are 100% sure that neither initialItems nor item.isSelected will never change on this component and is static. Could you explain to me why it would be considered bad practice.

@cosdensolutions

6 ай бұрын

It wouldn't be bad practice but in your example your value is static, not from the backend. If it came from the backend you'd have to fetch it in a component and then you need to do what I did in the video. But yes if it's just a random static variable in some file, sure you can do what you did. Even put selectedItem in that same file too and just import it

How does React know if "items' changes with looping through all 29mil items? Wouldn't that be the same performance issue we had? Thanks, great tutorial in general.

What is the difference between useMemo and useEffect? If we wrap the selectedItem function inside a useEffect like- useEffect( ( )=>{ const selectedItem=items.find((item)=>item.isSelected) },[items ] ) then it's serving the same purpose.

Super cool video. What is your Vs code theme

@cosdensolutions

7 ай бұрын

material theme darker

@davronmaxmudov3972

7 ай бұрын

Thanks bro @@cosdensolutions

Makes me think of react query. Prevents unnecessary api calls to your backend by multiple options to control fetches.

What will be the impact if we use useEffect in this example with selectedItem as another state? Apart from useMemo memoising the result. I am asking in this specific example?

@cosdensolutions

4 ай бұрын

It would be an extra state and useEffect to manage, plus another render cycle. It's always best to derive state whenever possible

Can we use multiple use effect in one component

Thanks! That's useful for me. And one ques it that may have some diff between use "const [item] = useState(initial)" and "const item = useRef(initial)" in ur case?

@cosdensolutions

6 ай бұрын

yeah there is a difference, check out my video on useRef to really understand!

@yuongeon1476

6 ай бұрын

@@cosdensolutions Thank for that, and can u make a video about Memo (not useMemo) cause i wonder when to use it

@cosdensolutions

6 ай бұрын

@@yuongeon1476 check out useCallback, I show it there!

In this case, if the count changes frequently and the re-render is only triggered by it, using useMemo here would be unnecessary. Right?

Hi Cosden, I do not figure out why do we need to use useState to wrap the initialItems. Does it make much sense?

@cosdensolutions

6 ай бұрын

Because the items can change over time and for that you need state!

But when you add count to the use memo dependency array, are you not now doing the find again on every click? Oh I guess this isn't a long running task now as its not searching through the whole array any more. But, doesn't that negate the reason to add useMemo in the first place?

@cosdensolutions

7 ай бұрын

Yep it does, but that's what you want. You don't want to prevent a re-compute, but rather control when it happens. You need the count to perform that operation so there's no way around it. However if you added a new state variable and changed that, then it wouldn't re-compute. It would without useMemo. That's the goal, to control and only when needed re-calculate!

Why is faster compare if the items array change than find function?