This list of different HTML elements all have a `testId` attribute added, which can be useful for extracting elements from the DOM for testing:

```typescript
<>
  <div testId="123" />
  <audio testId="123" />
  <video testId="123" />
  <a testId="123" />
  <abbr testId="123" />
  <address testId="123" />
</>;
```

However, there is currently an error for each since the `testId` attribute doesn't exist on these elements.

## Challenge

Your challenge is to find the correct interface to target, then use declaration merging in the global scope to add the `testId` attribute.

Keep in mind that this attribute should be optional, so it doesn't interfere with the rest of the environment.

Having an optional test attributes available can be useful for testing elements.

The first step for declaration merging is to use `declare global` with the React namespace:

```typescript
declare global {
  namespace React {

  }
}
```

Over in the React types, it looks like there are a couple different choices to try.

## `DOMAttributes`

Let's try `DOMAttributes`:

```typescript
declare global {
  namespace React {
    interface DOMAttributes<T> {
      solutionTestId?: string;
    }
  }
}
```

With this change we still have an error:

```typescript
All declarations of 'DOMAttributes' must have identical type parameters.

interface React.DOMAttributes<T>
```

This error tells us that we need to include the `<T>` even though it's unused:

```typescript
interface DOMAttributes<T> {
  solutionTestID?: string;
}
```

The errors have gone away, and the attributes have been added!

## `HTMLAttributes`

Another option is to use `HTMLAttributes`, which also uses the `<T>`:

```typescript
declare global {
  namespace React {
    interface HTMLAttributes<T> {
      solutionTestId?: string;
    }
  }
}
```

## `ARIAAttributes`

Finally, using `ARIAAttributes` will also work. Note that it does not require the `<T>`:

```typescript
declare global {
  namespace React {
    interface ARIAAttributes {
      solutionTestId?: string;
    }
  }
}
```

## Wrapping Up

While there are three different ways to add the `solutionTestId` attribute, my recommendation is to use `HTMLAttributes<T>` because it's the most specific. It also makes the most sense use HTML attributes in React.

Now that you have a clear understanding of the namespace structure and hierarchy of interfaces in React, you'll be better equipped to handle any errors that might arise in the future.

When you encounter issues with type parameters in React, remember to revisit this section and the concepts discussed here to help you resolve the problem!

Have a clear understanding of the namespace structure and hierarchy of interfaces in React, you'll be better equipped to handle any errors

Updating the Global Namespace for an Additional Attribute

[00:00] We're back on this DeclareGlobal. We definitely need that. We definitely need to use namespace react. Now it's a case of which interface do we use in order to add this solution test ID to it. We know that the base for a lot of this stuff, so it's going to be HTML attributes,

[00:17] which extends ARIA attributes and DOM attributes. We could, if we wanted to, put it on DOM attributes or ARIA attributes. Let's try DOM attributes first, so interface, DOM attributes, and let's just pull this out. But this is erroring here. Why would this be erring? All declarations of DOM attributes

[00:37] must have identical type parameters. And we can see that DOM attributes actually takes in a T here. So when you do like a global override like this, we need to make sure that we're getting the type parameters exactly the same. So this T, even if it's unused, it actually does contribute. So we need to make sure it's there.

[00:54] Now, we can have solution test ID, and we'll make it optional, and we'll make it a string here. So this ends up working. And this now means we have all of the DOM attributes that we need pulled in. Though this, I wouldn't say it's particularly perfect because I think, I mean, there's three different ways of doing this, basically,

[01:14] where we can have HTML attributes as the one we target as well. And HTML attributes, if I spell this wrong, by the way, just so you see, HTML attributes, it doesn't work because we've actually like missed out on the spelling here. And so the declaration merge doesn't work, but this one does work. HTML attributes ends up working.

[01:33] Lovely, lovely, lovely. And we've also got ARIA attributes as well. So ARIA attributes, is that spelled correctly? Must have identical type parameters. So I think we just remove this one because ARIA attributes itself doesn't actually take in a type parameter here. There we go. So now this works too.

[01:52] I always recommend using HTML attributes though. It just seems to make sense to me. And this means that like now this will be passed through into the DOM itself and we can strike this out with like Puppeteer or something similar. So this is really, really cool. And it means that we've kind of put all of the bits of information that we needed together,

[02:11] where we now can walk through the hierarchy of different interfaces inside React. We understand like how the namespace is constructed. And now whenever we get any errors that come up around this, we'll know where to go. And that's what I want you to take from this section. Thank you.

Add Attributes to All Elements with Declaration Merging

[00:00] Let's take everything that we've learned so far and put it into practice. Let's imagine that we wanted to add an optional attribute to all elements where we want to say, okay, we can pass this element a test ID. This test ID, it might just sort of like ping onto the DOM and it means that we can extract it out later and sort of pull it into our tests or things like that.

[00:18] So your job is to make use of declaration merging in the global scope and try to find the right interface to add this on in order to add it onto all of these props down here. And we want this to be optional as well, just so we don't, you know, muck up our entire environment here. Good luck.

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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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Add Attributes to All Elements with Declaration Merging

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