• Update state based on events
• Work with multiple state variables together

In the labs for this section, we'll be working on a grocery list app. Some of this app is already built out using static versions of the components. We'll be using state and events to make our app dynamic.

The components you have to work with are in the src/components folder. Start by examining these components and draw out your component hierarchy to see how data can be passed from one component to another.

In this lab, you'll update state and get more practice with the useState hook.

It's recommended that you run npm start and work on this in the browser before running tests. Try to get your app to match the demo! Once you've built out the components below, run npm test or learn test to see if your code passes the tests.

In the App component, there is a button for toggling between dark mode and light mode. Using the useState hook, create a state variable in the App component. Then, use that variable to determine if our app should be in dark mode or light mode.

You will also need to add an event handler to the dark mode button, and update state when the button is clicked.

The actual functionality of changing our app's theme is handled in CSS, so all you have to do is set up the code to update the className of the div based on your state variable:

<div className="App dark">
{/* for dark mode */}
</div>

<div className="App light">
{/* for light mode */}
</div>

In the Item component, when the user clicks the <button> element, the item should be added to their virtual cart. The way we'll show the user that the item is in the cart is by changing the className on the <li> element:

<li className="in-cart">
{/* the item is in the cart */}
</li>

<li className="">
{/* the item is NOT in the cart */}
</li>

If the item is not in the cart, the <button> element's text should read "Add to Cart", and if the item is in the cart, the <button> element's text should read "Remove From Cart". Naturally, you'll also need to add state to the Item component to solve this deliverable!

In the ShoppingList component, there is a <select> element that will allow us to filter the list of items by category.

Use the useState hook to create a state variable called selectedCategory for keeping track of the selected value from this <select> element. When the value of the <select> element is changed, update state.

You should also use the selectedCategory variable to determine which items to display in the shopping list. You'll need some way of filtering the array of items based on the selectedCategory.

• React Docs on useState