Generics: The most intimidating TypeScript feature
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- Опубликовано: 6 июн 2024
- Generics are a huge reason why TypeScript is SO DARN POWERFUL. Letting you create types from other types, pass types to functions, and even INFER those types without you needing to specify them.
They're pretty advanced, though - so if you want to learn more advanced TypeScript, time to strap in.
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www.totaltypescript.com/
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00:00 Intro
00:36 Generics on the type level
01:45 Passing type arguments to functions
03:06 Passing type arguments to Set
04:21 Inferring the types
05:55 Constraints on type arguments
08:19 Constraints in functions
10:07 Sometimes 'as' is fine
11:23 Multiple type arguments
14:05 Defaults in type arguments
15:00 Integrating with third-party libraries
17:26 Outro 
Кино
Matt, you are the Wizard. I can't describe how helpful this video was for me. It's purely golden. Thank you for your work!
Please never stop doing these videos, you're my inspiration
The stuff about apis is golden, I recently did a similar thing to stop typing JSON responses as 'any' and it really helped with leveraging Typescript to handle edge cases etc. I haven't used schema validation yet, but seeing how clean the code is, it's really enticing.
I have the task to write a blog post about generics and you, my lord, have completely saved me in the most important thing to do it, understanding them!
This is actually really awesome. The light bulb moment for me was "Take generic from inward to outward": as in, generics can be inferred from the arguments passed to a function. This is very poweful
Straight to bookmarks.
You're an amazing teacher!!
Brilliant video, learnt a lot - I've never really looked into generics before, so, now my Typescript knowledge really has gone up a level.
Great video. Not many new things for me. But it's really good to see someone making truly advanced topic videos on TS.
Keep it up 🚀
One of the best videos out there on Typescript Generics!
Thanks, Great video! Look forward to going through it in total typescript
I love you Matt, free contents that you produced are chef kisses. I am always craving for more.
Hey Matt, your videos are very helpful, you're covering features in TypeScript I needed and didn't know exist.
It'd be so great if you could give and example of a scenario before explaining a TS solution, for the more complicated ones.
Leaving out inline object types (like { firstName: string, lastName: string } would be nice too just so there's less to process heh.
The most helpful video I have seen for a while. :)
Adding to bookmark for using as a documentation.
What a wonderful video! I wish I can like it more than once. Thanks a lot Matt
Amazing video Matt, thank you so much!
amazing stuff Matt thanks for those tips🙌 they were really 🔥🔥🔥
that's it im sold. Subbing to this gold channel
best video i have seen in a while on yt. thankyou!
Nice video! Another tip is you can do generic type inference from a function return type, in the same way you can do it for function parameters
So nice video!! I’m starting with typescript so not sure if I get it well but what I understand is that generics help typescript to infer on the arguments we pass in a function and give the proper return type. So a well defined generic in a function will give a much easier function handling when using it. Sorry if it’s not clear for me just try to understand. Thanks anyway for this video will work on it.
bro this is wonderful you explained it VERY well
Love this Matt, thank you so much
Great Tips. thanks a ton Matt.
Many cool pieces of advice. Thank you!
Amazing Matt ... Just Amazing !!! Thanks
very clear explanation, amazing
Always A+ content. Thanks for this!
Thanks very much for the video. This is a real eye opener.
Excellent tips, thank you!
Thanks for sharing, great tips and I didn't know much about generic types.
I just fear huge overheads, especially in the code readability department. When these types of codebases are written in real world scenarios, things turn pretty ugly pretty quickly.
And usually, when the wizard who wrote this dark spells on a magic mushroom microdose induced flow state goes for the better paying company, the rest of people is left scrambling in chaos.
Sometimes, especially for large companies with mixed teams, it's ok to be a bit verbose and repetitive if it leads to faster handovers and a better overall team experience.
That said, we (as the JS community) need to mature towards more advanced design patterns.
Was great learning about generic types today, thanks for sharing!
In general, you'll mostly see generics, conditional types, the "infer" keyword, etc used in packages to make them as strictly typed but broadly usable as possible. In real-world production code, I would indeed avoid complex types and be more verbose about your typing.
This is awesome Matt 🙌🏻
Thank you for the effort to make this awesome and useful video, Much love
This man is on another level! Subbed!
This video makes me love more typescript!
Thanks man, very good content.
The more I watch your videos I love TS more! 🧡
Hey Matt,
I've been following you on X for sometimes and learned a lot from about TS.
And here as well.... Subscribed 😍
Really good explanation! 👍
Like and subscribed. Awesome tips, they proved to be particularly useful for me just to learn.
Nice work Matt
Tip 10 is the best one! Just did something similar the other day.
Outstanding. Last time I used generics was C++ and Java in the late 90s probably before most of the other commenters were born😂 and it’s really great to see the inference capabilities to avoid “type stuttering” you otherwise get.
Thank you Matt for all this great content! May be consider slowing down a bit so we get time to grasp the content and avoid head spinning injury by having to rerun videos/ play at lower speed with robot voice 😀
Great video!
this video is just immensely helpful
Great video, Matt. Hats off ;)
Thank you Matt!
great, direct into the point
Legend! thanks mate, the best of the best of the best :) 🙏🏼
I'm in love with that makeZodSafeFetch function! Thank you for this great video!
Amazing! Thnx Matt
I love this video so much !
Coincidentally, I just watched your generics video on LWJ and was doing those exercises. This is a great video. Lot of things clicked for me with generics! Thanks Matt!
What's LWJ, if I may ask?
@@andyl.5998 Learn With Jason www.youtube.com/@learnwithjason
@@andyl.5998 Learn With Jason, if you haven't found it already
Superb video
this is absolute masterclass...
Man, you are the sunshine!
14:03 is the better part of this video 😁
Thankyou this was super useful :)
Thank you so much man you are great, bless you.
spectacular tips
I pressed the like button, I got a surge of dopamine 👍. Really interesting video, generics are fun!
This is gold 🔥
You are so cool while explaining!!!
Dang. That was good. Thanks for making this.
I just love final part imo
Great video
Wow. What a helpful video.
Thanks for the videos Matt. I can imagine they take a lot to put together. Just something I've noticed, you speak really fast and take almost no breaths between words 😅 then you go from one topic to the next with almost no breaks in-between. For me personally It's really tough to follow because these are kind of complicated topics you are covering. Again, I really appreciate the time and effort you put into your videos. Just a bit of constructive feedback from one viewer. 👌🏾
At 14:00 I laughed so hard. Really good explanation of generics. Good job.
Yeah right, the guy really likes Generics LOL!
I usually don't make comments, but this was a great video. Thank you !
This video singlehandedly dissolved my fear of "complicated" typescript. I'm pretty new to it, but now I want to use generics everywhere
This video is exactly what I needed!
P.S. it’s still really hard for me to get over the fact that non-Chinese people don’t know how to count to 10 on one hand.
Hey Matt, another great video! In the end of the video you still have to create a zod object of the type specified. Can you make zod infer the object from the schema and implement it?
This was a brilliant video. You are clearly incredibly knowledgeable in all things typescript so instead of just giving praise I'd offer a tiny bit of criticism, maybe it's worth something too you, maybe not.
Ive watched all your videos, some multiple times, and the one thing I notice is that some examples are a little too contrived, or at least it's not clear where I'd ever use a certain tip. Ive been a professional ts dev for about a year, and I'm no where near as good as you are but I really struggle to see the use cases in some of the tips, I'm not saying they don't exist, it's just I can't see them. Your zod example is a perfect example of the type of tips I find most useful, it's clear the real world use case and the example you use is a something we might actually see in our own code bases. Basically I'm saying is love some more real world examples for some of the more complex tips you give. I think part of it is your older videos were quite short which are great for a quick look and you do a great job of explaining how it works clearly, but then the video just ends and I'm left wondering how to apply it somewhere.
Overall 9/10, just thought this might be more useful just another clap emoji. Thanks for your videos, looking forward to the next one as always.
That's interesting! I've heard this criticism before but I consider this video to be a good example of me using real-world examples. Type safe object keys, typing Set, making type-safe fetches, integrating with Zod are all things I've been asked how to do. Which example in particular felt too abstract for you?
good feedback ≠ criticism
i wish i'd seen this video like four months ago, when i refactored an entire routing architecture, for which i found myself using what here you will see as tips 1 through 9.
Had to learn it the harder way. this video would have really made the learning curve less steep.
I
Default params in TS o.O Whaaaaaaaaaaaaaat ? Matt, tip after tip and I think you can't amaze me more and there you go :D Matt, you're our hero 🍻
Hi Matt, great content as always, may I ask what extensions or settings you have that allows inlay hints to popup where there is "// ^?"
Twoslash Query Comments
I am really glad that I started my javascript journey with Typescript. Thank you so much for the video.
Did you invent Typescript? Lol. Just kidding. I watch your videos all the time. Very enjoyable.
Which extension is it which is giving type hints using "^?"
Yup I would love to know this also
twoslash-queries vscode extension.
@@nextmaker Thank you for this link :D
Hah nice, Matt just posted a video about this extension!
Chdck his most recdnt video
Amazing video! Thank you!
One question tho, for tip 7 (10:07) wouldn't casting as Array potentially give wrong types (and thus potentially wrong linting) if some of the keys of the object are not defined as strings? Since Object.keys returns strings and even if the key is not a string (e.g. number) it's converted to a string, but `keyof TObj` doesn't convert to string and keeps the original type. In the example, that problem doesn't come up since both the "name" and "age" keys are strings, but for e.g. { name: "John", 42: "whatever value" }, if you later try to do some string-specific operation on `result`, like `result[1].charAt(0)`, the IDE will flag it as something like `Property 'charAt' doesn't exist on type '"name" | 42'`, when that's a perfectly valid thing to do since Object.keys will return the string "42" for the number key 42
You're right.
10:07 To get the proper return type of your function, instead of type assertion, you can add it as return type to the function:
const typeObjectKeys = (obj:TObj):Array =>{
return Object.keys(obj)
}
This would result in the perfectly valid error of "Type 'string' is not assignable to type 'never'", since empty arrays can be passed to it. Since keyof keeps the original type but Object.keys returns strings, this can cause runtime errors.
The proper implementation would assure that only objects with valid keys can be accepted by the function:
const typeObjectKeys = (obj:TObj):Array =>{
return Object.keys(obj)
}
Hi, is there any difference between 'object extends T' and 'T extends object'? If so, what could be an example to best illustrate a use case for one vs the other?
Default type parameter is actually genious feature
What plugin are you using that displays the result // ^?
Really great content! Please provide a Nextjs 14 course. I follow stephen grider, but your way of teaching impressed me.
I would like to work for free for you! I want to improve my coding!
Amazing job! Don't want to under estimate your workshop because I know it is excellent quality based on your videos and it requires a lot of work to put something with this quality together, I was wondering if there is any discount for students?
7:43 Any difference between doing that and doing extends Function?
@Matt, do you know why in example N8 (getValue function) we need explicitly provide the second generic for the keys - 'TKey extends keyof TObj'? Why the setting of the arg 'key: keyof TObj' is not enough?
I'll attempt to answer in the absence of Matt. The issue is how to get TS to connect the return type with the input type. Since the input type is an object with multiple attributes, each with a different type, we don't want the return type to be a union of all those possible types, we want it to be keyed to the 'key' input arg. Hence we use the 2nd generic and infer the return type. On a deeper level, I'm uncertain "why" this is necessary, why TS didn't have enough information to start with. Which is something for Matt to explain.
@@jasonstewart7983 Thank you
Question: What is the // ^2 in your code, and why it log the variable all the time ?
Is it a plugin or typescript external ?
Its a VSCode extension. He covered it in this video before:
ruclips.net/video/u0adKDu--cA/видео.html
Nice content, we are using it a lot with react applications. I will ask why in part of generic we need to write like instead a simple . Thanks for sharing your knowledge:)
Because in .tsx files is parsed as a JSX node, but isn't.
13:34 nice! this is useful stuff
Clicking "like" because I really need those generics in my brain
let me grab a beer to make my fears go away and jump fully into this, is ok to have fear, but I need to face it
How to make type argument required? That createSet() should throw a type error about missed type argument?
crazy good
Generics are so cool!
everytime I try to use keyof in generics I end up with it staying at the union type. Yesterday I was trying to merge all my getBundledFooBar functions into a single util and it just never wanted to work for me. Really confused as to what specifically makes typescript understand when a keyof-based parameter is not the union of all keys.
This seems like a more powerful form of destructuring, where instead of presetting the initial values, you enforce the types that should be returned.
That was great but you did one mistake in tip 7 you don't need to use "as" in that example if you restrict the type of the object to have keys of type string. Object.keys doesn't return symbols in JavaScript but the keyof does.
const typeObjectKeys = (
obj: TObj
): Array => {
return Object.keys(obj);
};