4 ways to use the TypeScript infer keyword

I've always been a little baffled by TypeScript's `infer` keyword? So I explored the ways you can use it, and came up with 4 variations! If you have other fun examples of how to use `infer`, let me know in the comments!

0:00 - Intro
0:32 - Generic Arguments
2:25 - Arrays
4:37 - Function Parameters and Return type
7:03 - Template Literals
9:53 - Outro

[stonecoldcold]

I've always never understood infer. But the examples you have shown is the best that made me understand finally.

[ДаниилСоболев-щщ]

That is the best explanation of infer ever.
It is not fair.
Why shitty stuff like "BECOME A FRONTEND DEVELOPER IN 5 SECONDS" is much more popular...

[dimitargetsov]

Two reasons to remember and share this channel with anybody:
1.content (on TS) second to none.
2.family name -Burgess--same as of Antony Burgess--"Clockwork Orange".

[the_proletariat]

This was cool. I didn't know anything about infer. Thanks to your video and challenges, now I know. Keep up the good work!

[kyuubyemy]

My implementation of FirstParam and SecondParam:
type FirstParameter<T extends (...args: any[]) => any> = T extends (firstParam: infer A, ...args: any[]) => any ? A: never;
type SecondParam<T extends (...args: any[]) => any> = T extends (firstParam: any, secondParam: infer A, ...args: any[]) => any ? A: never;

Also Jojo is everywhere LMAO

[serglohm]

Great job! This is definitely the best video about infer on 2022!

[vishwajeetraj]

This was Epix.
Looking out for more.

[vihanv]

Wow! This has got to be the best video on the infer keyword I've ever seen. Keep up the good work Andrew! Liked and subbed 😀

[AiguretDuren]

This was legitimately fun to code along with. Thank you!

[i.j.]

Really nice demonstrations. Thanks a lot! It really made me understand the infer keyword better!

[이지용-gw]

This was the best explanation for infer. Cheers!

[devinorium]

Upped the production quality. Looks dope

[johnyepthomi]

Dayum. This is very useful. Thanks for sharing.

[joshreynolds]

Great explanation on this. Infer is so powerful

[УДжорджа]

What a great explanation, thank you so much!

[shayanpaul]

I have a question related to testing whether two types are equal or not. The utility type in @type-challenge is as follows :

export type Equals<X, Y> =
(<T>() => T extends X ? 1 : 2) extends
(<T>() => T extends Y ? 1 : 2) ? true : false;

Maybe it a very basic or idiotic question but i am unable to understand from where this T type parameter is coming from and what will be its values

[ffedchik]

Awesome content. Keep up the great work!

[samirnayibruza]

You could do something like this instead of using overloads on functions:

```ts

interface Item {
id: number
}
interface FindOptions {
one: boolean
}
declare function find<Options extends FindOptions>(options: Options): Options extends {one: infer FindOne} ? FindOne extends true ? Item: Item[] : never

const item = find({one: true}) // Item
const items = find({one: false}) // Item[]

```

Edit:

After a few minutes I realized that in the above case there is no need because I could just do `Options extends {one: true}` directly but imagine the possibilities 😁

[MohamedRagab-kpbp]

type MyParameters<
T extends (...args: any[]) => any,
I extends number
> = T extends (...args: infer A) => any ? A[I] : never;

[yujitomita]

Thank you for this. Agreed with Jimmy this is hard.