Here's the `fixedForwardRef` function from the previous lesson:

```typescript
function fixedForwardRef(
	render: (props: any, ref: any) => any
): (props: any) => any {
	return forwardRef(render) as any;
}
```

Currently it uses the `forwardRef` provided globally by React, but we want to change it to use a local function instead.

We want to use a local function because overriding globals isn't a great idea in a library setting, as it could cause issues for your users downstream.

## Challenge

There are a couple different ways to change `forwardRef` to use a local function.

One way will look similar in structure to the `fixedForwardRef` function. Another way will do it all on the type level.

Hint: Follow the trick you saw in the previous explainer video about using `forwardRef` with generics. You can even just copy the code over!

When overriding global behavior, it's best to do it locally to prevent conflicts in library development scenarios.

For the first solution, let's start by looking at the actual `forwardRef` type from the previous explainer code:

```typescript
declare module "react" {
	function forwardRef<T, P = {}>(
		render: (props: P, ref: React.Ref<T>) => React.ReactNode
	): (props: P & React.RefAttributes<T>) => React.ReactNode;
}
```

We can see that `forwardRef` takes in a `T` for the type and `P` for the props that we want to represent in the ref.

Now, let's copy the render function into the `fixedForwardRef` function:

```typescript
function fixedForwardRef<T, P = {}>(
	render: (props: P, ref: React.Ref<T>) => React.ReactNode
): (props: P & React.RefAttributes<T>) => React.ReactNode {
	return forwardRef(render) as any;
}
```

We have `props`, which represents `P`, and the `ref`, which is a `React.Ref` that captures the thing we're referencing. The render function takes in `P` and the `React.Ref` attributes and returns a `React.ReactNode`.

Now everything starts working beautifully and we've got a local declaration for our `forwardRef`, except we've added an extra function on top of it.

The cooler solution is doing a manual override.

## Overriding `forwardRef` Manually

Instead of having a `fixedForwardRef` function, this version uses a type:

```typescript
type FixedForwardRef = <T, P = {}>(
	render: (props: P, ref: React.Ref<T>) => React.ReactNode
) => (props: P & React.RefAttributes<T>) => React.ReactNode;
```

Then the key line is this:

```typescript
const fixedForwardRef = forwardRef as FixedForwardRef;
```

Now the `fixedForwardRef` does everything that our global scope function did, but it's local and contained within the code block.

This approach is recommended if you want to prevent logic from bleeding out into any code that consumes it.

Override forwardRef's Behavior Locally

[00:00] Okay, this is a pretty simple exercise in copy-paste. Let's go and grab the actual type from here, and let's just copy this over. We know that this is going to take in a T and a P, which is basically representing the props here. And T is going to represent the actual type of the thing that's being passed in,

[00:19] or the type that we want to represent in the ref. So now we can take that render function there and basically copy and paste this over. We have a props here, which is representing P, and the ref, which is a react.ref, capturing the thing we're reffing. Then we want to return a function,

[00:38] which basically takes in P and the react.ref attributes and returns a react.react node. So let's copy that over, grab that there, and let's bung that in there. Now things start working. Beautiful, beautiful, beautiful. And we've got essentially just a local declaration for our forward ref.

[00:55] But there's actually a cooler solution than this, because this is actually adding just an extra function on top here, which we don't necessarily need. What we can do instead is we can just actually override it manually. So we can say, let's say, just don't save that, that's fine. Now what we've got, we've got a fixed forward ref here,

[01:15] and this is a type that's representing exactly the same thing as we saw in our previous setup here. So we've got a render function here. Let me just sort of pull that down below my face a little bit, there we go, which is basically just representing the type of our fixed forward ref here.

[01:32] And what we're doing is we're now saying forward ref as fixed forward ref, which behaves in exactly the same way. Whoops, I forgot to import these use refs there, dammit. Now this fixed forward ref just does all of the thing that we had captured in our big, beautiful global scope function there, but it's just local.

[01:51] And again, I think this is the way to go if you don't want this to bleed out into anything that consumes this code.

Fixing forwardRef Locally

[00:00] Using the previous exercise as a guide, I want you to actually change forward ref instead of using the global definition, let's actually use this definition here. Let's actually make it a local function. And what I want you to do, you can approach this kind of creatively. There's one solution that uses this format,

[00:19] but there's another solution that does it all on the type level. I kind of want you just to take this function and type it according to the trick that you saw in the previous exercise in the forward ref with generics explanation. Now you can just go and look at the code and copy that over. That's definitely the way to do it. I don't want you to necessarily have to find the solution yourself,

[00:39] but hopefully by doing this, you will get a stronger sense for like how it works. But also this is probably the solution you should use if you're doing library stuff as well, because you probably don't want to be overriding the global in a library setting because then your downstream users might end up with that in their projects. So this I think is actually the solution

[00:58] that I would use from those situations. But anyway, I've given you enough. Good luck.

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Type-Checking React Props With Discriminated Unions

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Manage TypeScript's control flow limitations in discriminated unions with destructuring: balance prop access and discriminator narrowing.

Destructuring vs Accessing Discriminated Union Props

Destructuring Discriminated Unions in React Props

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

Differentiating Props With a Boolean Discriminator

In this exercise, you will learn how to use the Record type to represent an empty object by passing in a string and never type.

Using the Record Type to Represent an Empty Object

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Allow Optional Props Using A Discriminated Union Branch With Undefined Types

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Learn what makes these two React types different and how to use them effectively to ensure type safety in your code.

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Finding a Better Type Definition For A Mapped Component

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The `keyof typeof` pattern in TypeScript to derive types from variables and create dynamic maps for runtime behavior.

The `keyof typeof` Pattern

Syncing Types without Manual Updates

There is a quirk in TypeScript where autocompletion for types with predefined values and strings doesn't work quite as you might expect.

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

Using `as const` and indexed access types helps you extract keys and values from a type.

The combination of `as const` and indexed access types allows you to extract keys and values from a type.

Using `as const` and Indexed Access Types to Extract Keys and Values from a Type

Extracting Keys and Values from a Type

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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

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

Inference from a Single Source of Truth

Advanced Props

Generics and type helpers combine to create reusable code that's easy to understand and maintain.

A generic type helper makes our code more reusable and easier to understand.

Implement a Generic Type Helper

DRY out Code with Generic Type Helpers

Refactor complex type logic into a type helper.

An "All or Nothing" type helper simplifies complex logic while allowing for flexible object shapes.

Creating an "All or Nothing" Type Helper for React props

Refactoring to 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.

Add Generic Constraints to Type Helpers

Constraining a Type Helper to Accept Specific Values

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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.

Adding Type Arguments to a Function

Adding Type Arguments to a Hook

Learn how TypeScript behaves when wrapping one generic function inside of another generic function.

TypeScript uses type inference to infer the type of generic functions, making them easier to use.

Type Inference with Generic Functions in TypeScript

Wrapping a Generic Function Inside of Another

Generics are useful for components, especially in situations where different props depend on each other.

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

Add a Generic Type Argument to a Props Interface

Applying Generics to Components

There are still class components in legacy codebases, so it's important to understand how to make them generic.

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

Converting a Class Component to be Generic

Generics in Class Components

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In order to get proper inference, the type arguments need to be passed appropriately to the type helpers.

Use the Angle Brackets Syntax to Pass a type to a Component

Passing Type Arguments To Components

Generics enable the useful pattern of inferring type arguments through multiple different type helpers.

Adding Generic Type Arguments to Type Helpers

Generic Inference through Multiple Type Helpers

Discover how to optimize your code by making use of generic hooks and type constraints in useMutation. 

Comparing function arguments rather than the functions themselves should be considered a best practice when dealing with function assignability in TypeScript. 

Refactoring a Generic Hook for Best Inference

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Generics aren't always the best solution for every problem. Sometimes, a different approach is better suited for the task at hand.

Replacing generics with a discriminated union can make your code cleaner and easier to understand while still maintaining the same inference.

Refactoring from Generics to a Discriminated Union

Generics vs Discriminated Unions

Using Generics with Components

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Use 'as const' to Infer a Tuple return type

Fixing Type Inference in a Custom React Hook

Learn how to create a strongly typed context in React using the createRequiredContext function, and fix type errors that can occur

Avoid the common issue of creating a context and not knowing what to pass into it.

Using Type Arguments to Create A Strongly Typed Context

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Learn a pattern for managing complex state that helps you track every possible state your application can be in.

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

Handling Complex State Management with TypeScript Unions

Using TypeScript to Manage Complex State

Clever usage of TypeScript types provides a great alternative to useReducer for tracking multiple properties in state.

Learn how to use discriminated unions with useState to effectively manage different states and properties in your React applications.

Handling Different State Values with Discriminated Unions

Using Discriminated Unions in useState

Learn how a different type signature can lead to better inference when working with different statuses in React state.

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

Improved Type Safety with Discriminated Tuples in TypeScript

Discriminated Tuples in Custom Hooks

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Overloading Functions in TypeScript

Use Function Overloads for Better Type Inference

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Be careful when using function overloads, because it's easy to end up in an impossible position and TypeScript won't warn you about it!

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Advanced Hooks

React provides a namespace that contains types, functions, and values. Type definitions can help you understand why and how React works the way it does.

The DefinitelyTyped contributors have structured the React types so that they work in both the runtime and type worlds.

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Exploring the React Namespace

React gives us a few different types to use for our components. Understanding the differences between them can help you avoid errors and write better code.

Learn how JSX.Element, React.ReactElement, and React.ReactNode affect type inference and return values in React components.

Understanding React's JSX Types

JSX.Element, React.ReactElement, and React.ReactNode

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Manually call JSX to force the type of children passed to a component to be a specific type.

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JSX.IntrinsicElements is a global interface that contains HTML attributes as properties that you'll when using TypeScript in React.

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Types Deep Dive

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It's important to understand constraints when typing third-party libraries.

Strongly Typing Lazy Loaded Components with Generics

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Infer Shared Props for Multiple Components

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The Problem With forwardRef

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By making an HOC generic and properly handling the props it is passed, we can create a more flexible component.

Implementing a Generic Higher Order Component

Typing Higher Order Components

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By updating type signatures and changing how props are handled, we can make a Higher Order Component that works with generic components.

Add Generic Component Support to a Higher Order Component

Using Higher Order Components with Generic Components

The `as` prop is one of the most complex in TypeScript, and there are lots of different ways to approach it.

Explored here are two approaches to the `as` prop in React, with one much more efficient than the other.

Transcript

Fixing forwardRef Locally

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