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

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!

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

The best useMemo explanation I've seen.

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

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

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

Wow... perfectly explained man, Thanks.

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

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!!!

Really useful tutorial. Thanks for being so helpful!

You have the best tutorials channel 🙌🙌🙌🙌

Simply explained indeed, Thank you.

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.

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 :)

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

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

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

So good! You explained it perfectly!

So simply explained! wow, amazing

you are THE BEST to explain!

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

Best explanation ever. understand in one go.

this was a perfect explanation - thank you!

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

that was very helpful, thank you for clearing the confusion

the most clear explanation!

Great explanation, thank you!

Thank you for your clear explanation ❤

great explanation, thank you very much!

Best tutorial for useMemo!

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

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

This guy is the best teaching react stuff

Very well explained!

Wonderful !! 👏 I subscribe right away !

Once again great tutorial...

Awesome...very well explained

Thank you, great explanation

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

Well explained Thank you very much.

Great explication bro. Thank you very much

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

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.

Great explanation!

awesome explanation, thanks

Ohh man nicely explained 🎉❤

This video helped me a lot.

Appreciate your explanation ! thanx

thanks alot , very helpful🌹

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..!😊

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.

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.

Good stuff, thanks

Great one!! thanks bro

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!!!

Best video ever❤❤

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

Really its a Last Usememo video for me🥰🥰🥰

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

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 :)

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

Thanks, man

youre an react angel haha,awesome bro,thank you

Well explained

best teaching

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

God tier video

thank you so much

Thanks man

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?

Thanks a lot!

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

Thank you

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

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

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

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

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

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.

Ty bro

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.

Can we use multiple use effect in one component

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

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

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?

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.

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?

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

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.

I don't understand how is it optimizing performance when using const selectedItem = useMemo( () => items.find((item) => item.id === count), [count, items], ); when I only have count and items state in component. any how whenever one of them change selectedItem recomputes.

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?

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?

so what is the difference between useEffect and useMemo , by looking this example I felt we could do the same thing with useEffect , cant we ??

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.

Hello their, your video is just clear the useEffect. I copied your code and observed it is showing The couunt is 0 THEN I am been cleand-up THEN The couunt is 0 on refresh the page. Why so?

Great but cant I use useEffect instead? like it also has the dependencies array, and only runs once guaranteed if items dont change.

Can't we accomplish the same thing using useEffect? Can someone explain the difference of using these two hooks in this scenario?