In this exercise, we're going to bring together several of the TypeScript concepts that we've seen so far.

Here we've got a `buttonPropsMap` object, which contains various button variants organized into three categories: `reset`, `submit`, and `next`:

```typescript
const buttonPropsMap = {
  reset: {
    className: "bg-blue-500 text-white",
    type: "reset",
    // @ts-expect-error
    illegalProperty: "whatever",
  },
  submit: {
    className: "bg-gray-200 text-black",
    type: "submit",
    // @ts-expect-error
    illegalProperty: "whatever",
  },
  next: {
    className: "bg-green-500 text-white",
    type: "button",
    // @ts-expect-error
    illegalProperty: "whatever",
  },
};
```

These variants are then incorporated into a `ButtonProps` type by using `keyof typeof`:

```typescript
type ButtonProps = {
  variant: keyof typeof buttonPropsMap;
};
```

However, we have an error on `button` where the types don't seem to be correctly assigned:

```typescript
const Button = (props: ButtonProps) => {
  return <button {...buttonPropsMap[props.variant]}>Click me</button>;
};
```

The error message is really long, but it's going to be helpful for us to understand what's going on:

```typescript
Type '{ 
  children: string; 
  className: string; 
  type: string; 
  illegalProperty: string; 
} | { 
  children: string; 
  className: string; 
  type: string; 
  illegalProperty: string; 
} | { 
  children: string; 
  className: string; 
  type: string; 
  illegalProperty: string; 
}' is not assignable to type 'DetailedHTMLProps<ButtonHTMLAttributes<HTMLButtonElement>, HTMLButtonElement>'.

Type '{ 
  children: string; 
  className: string; 
  type: string; 
  illegalProperty: string; 
}' is not assignable to type 'DetailedHTMLProps<ButtonHTMLAttributes<HTMLButtonElement>, HTMLButtonElement>'.

Type '{ 
  children: string; 
  className: string; 
  type: string; 
  illegalProperty: string; 
}' is not assignable to type 'ButtonHTMLAttributes<HTMLButtonElement>'.

Types of property 'type' are incompatible. 

Type 'string' is not assignable to type '"button" | "submit" | "reset" | undefined'. ts(2322)
```

## Challenge

Your task is to identify and resolve this error by using `ComponentProps` and other techniques we've seen so far.

The categorization of `next`, `reset`, and `submit` buttons should be maintained, and any illegal properties need to show errors. You should also be able to autocomplete properties as expected.


First things first, we need to discern a type for our `buttonPropsMap`.

## Typing the `buttonPropsMap`

We'll define a type called `Map` which will be a `Record` with a `string` key and a value of `ComponentProps<"button">`.

```typescript
type Map = Record<string, ComponentProps<"button">>;
```

This `Map` type is essentially an index signature on an object, which is a string. Then the `React.DetailHTMLProps` represents the `button` props. 

Now we can apply the `Map` type to our `buttonPropsMap`:

```typescript
const buttonPropsMap: Map = {
   ...
```
With this change, we're now getting autocomplete inside the `buttonPropsMap` and all of the illegal properties have disappeared.

However, there's a snag.

## Fixing the `variant` Error

Our `variant` has stopped working. It's being inferred as a string, instead of `reset`, `submit` or `next`:

```typescript
// inside the Parent component's return:

{/* @ts-expect-error */} // not erroring like it should!
<Button variant="something"></Button>
```

The key inside of the `Record` is actually crucial to understanding this issue.

Here's what we currently have:

```typescript
type Map = Record<string, ComponentProps<"button">>;
```

Manually specifying the keys for the variants would fix the issue:

```typescript
type Map = Record<"reset" | "submit" | "next", ComponentProps<"button">>;
```

However, this isn't a great solution because it the variants aren't actually being inferred, and they are specified in two different places since `buttonPropsMap` is being specified as the `Map` type while also containing the variants.

As we've seen before, the way to get around this is to use `satisfies`.

## Using `satisfies` to Ensure Correct Inference

We'll remove the annotation on `buttonPropsMap` and use `satisfies` instead. We also can remove the `Map` type and specify the `Record` directly:

```typescript
// before:
const buttonPropsMap: Map = {
   ...
}

// after:
const buttonPropsMap = {
   ...
} satisfies Record<string, ComponentProps<"button">>;
```

Using `satisfies` ensures that our `button` variant satisfies the `Record` without overriding the type. 

This gives us the `reset`, `submit`, and `next` variants, and can be used in the component along with autocomplete:

```typescript
// hovering over buttonPropsMap

const buttonPropsMap: {
   reset: {
      className: string;
      type: "reset";
      illegalProperty: string;
   }
   ...
```

Using `satisfies` lets us avoid duplication by inferring everything from a single source of truth.

Discover the power of keyof and satisfies to ensure type safety while maintaining a single source of truth for your type.

Understanding and Implementing Dynamic Props Mapping in React

[00:00] Okay, let's see if we can solve this. This button props map here, we need to first of all just figure out a type that would even represent what this is trying to do here. It's kind of like a record or a map where the keys are component props button. So let's try and figure that out first.

[00:18] Let's say type map for instance, equals a record and let's say string and now component props button here. So we've got this map and this looks good. I mean, this is a pretty horrible readout, but this is essentially what it's doing. It's an index signature on this object, which is a string.

[00:36] And this huge React detail HTML props is just essentially an interface here that represents the button props. So we've got our map. Let's now take that map and use it on our button props map. So we've got map down here and this is really great. We're now getting auto-complete inside here.

[00:55] The illegal properties have disappeared and it all seems well. Now inside our button here, we've got button props map props.variant and this all seems good too. But there's something wrong here. There's a single error. And this single error is the key to understanding this exercise

[01:13] because now our variant has stopped working. This variant here, key of type of button props map is being inferred as a string, not as reset, submit or next. So this string here, the key inside of record is actually kind of key to understanding this. So we've got this record.

[01:32] Now record here, we could actually manually type this. We could say reset or we could say submit or we could say button down the bottom. And okay, this now works here. Or does it work? No, because I put next or put button instead of next. This works.

[01:53] And it means now that the variants down the bottom are all working. We've got next, reset and submit. Yay! Except this variant is now kind of lame because or rather this setup is really lame because we now have reset, submit and next, but they're not being inferred.

[02:12] We now have this duplicated in two places. Wouldn't it be great if we could infer one from the other? Well, there seems to be no way around this because it's kind of circular, right? This is being typed as map and this is being sort of typed before we even get to map. Well, there is a way around it. Let's put string back in here and we're going to take this

[02:32] and we're going to actually just delete this annotation. And just like in another exercise in this section, we're going to use satisfies here. And satisfies, what it's going to do is it's actually going to make sure that it satisfies that record string component props while not overriding the type. Yes!

[02:50] So now we get reset, submit and next. And we've got these two types inside here, which means that we can then use them later to figure out this variant down there, which is just perfect. So we've still got the autocompletes here. And it means now that if we add a new one to this,

[03:08] then we're still going to get autocomplete in here too and it's still going to be inferred down. So this means satisfies is a really, really nice way when you combine it with key of type of to actually still retain the responsibility principle for your types, a single source of truth, while still making sure that you can get autocomplete

[03:27] on that source of truth.

Inference from a Single Source of Truth

[00:00] In this exercise, we're combining a few things that we've learned together. We have this button props map kind of object here, which has a bunch of different variants of buttons. So we have our reset button, our submit button and our next button, like in a multi-step form. And in our button props, we're taking that variance and we're putting them in here.

[00:19] But there's an error kind of below here where we're not getting the right types in, it seems. So your job is to figure out what this error is. We also want to make sure we retain this kind of next reset and submit thing. And we want to make sure that these illegal properties start erroring.

[00:38] So you're going to need to find a type, again, possibly using component props and using some other stuff that we've seen before, to type button props map correctly so that we get rid of these errors, get rid of this error, and we still get the nice autocomplete below.

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You'll need a working knowledge of React, as well as foundational TypeScript knowledge. Working through the [React with TypeScript Tutorial](https://www.totaltypescript.com/tutorials/react-with-typescript) is recommended.





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Destructuring vs Accessing Discriminated Union Props

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Learn how to add a required React property to different variants of a discriminated union in TypeScript

A guide on how to properly use intersection to resolve union types in TypeScript and ensure code readability.

Resolving Discriminated Union Types with an Intersection

Adding a Prop Required Across Discriminated Union Variants

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Learn how to use discriminated unions to handle conditional props in TypeScript.

Discriminated Unions for Conditional Props in TypeScript

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Allow Optional Props Using A Discriminated Union Branch With Undefined Types

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The `keyof typeof` Pattern

Syncing Types without Manual Updates

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Wrap the string in parentheses and intersect with an empty object to resolve the partial autocompletion quirk in TypeScript.

Solving Partial Autocompletion

The Partial Autocompletion Quirk

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Differentiate between annotation operators, "as const", and "satisfies" in TypeScript for optimal type inference and validation based on specific use cases.

Comparing `as const`, `as`, and `satisfies`

Ensuring Correct Inference for Prop Types

Advanced Props

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Implement a Generic Type Helper

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Refactor complex type logic into a type helper.

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Enforcing constraints helps you prevent errors from occurring, and ensures your type helpers are being used in the correct way.

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By default, type arguments are inferred as `unknown`. When using this type of API in your code, it is crucial to have it well-documented.

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Type Inference with Generic Functions in TypeScript

Wrapping a Generic Function Inside of Another

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By adding a generic type argument to a props interface, we can infer prop types.

Add a Generic Type Argument to a Props Interface

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Props work the same whether we're using functional components or class components. It's just the generic syntax that's different.

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Learn how to properly type complex React state that represents different possibilities using TypeScript.

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Discover how using discriminated tuples in TypeScript gives better inference as demonstrated through an example involving loading, success, and error states.

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Use Function Overloads for Better Type Inference

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Inference from a Single Source of Truth

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