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React Controlled Components Lab

Learning Goals

  • Implement a controlled form

Introduction

In this lab, you'll write and use controlled components.

Controlled Components

Now that we know how to handle form elements in React and how to set up controlled components, it's time to put that knowledge to the test. This lab is fairly extensive, but you'll use many core React concepts here that will surface again and again. Time to get some practice in!

We'll continue adding new features to the Shopping List app using controlled components. Make sure to familiarize yourself with the code before diving into the deliverables! Completing these deliverables will also require understanding of all the previous topics from this section, including initializing state, passing data and callback functions as props, and working with events.

Deliverables

Filter

In the filter component, there is a new input field for searching our list. When the user types in this field, the list of items should be filtered so that only items with names that match the text are included.

  • Determine where you need to add state for this feature. What components need to know about the search text?

  • Once you've determined which component should hold the state for this feature, set up your initial state, and connect that state to the input field. Remember, we're trying to make this input a controlled input — so the input's value should always be in sync with state.

  • After you've connected the input to state, you'll also need to find a way to set state when the input changes. To get the test passing, you'll need to use a prop called onSearchChange as a callback.

  • Finally, after making those changes, you'll need to use that state value to determine which items are being displayed on the page, similar to how the category dropdown works.

Note: you may be asking yourself, why are we making this input controlled when the <select> element is not a controlled input? Well, the <select> input should probably be controlled as well! The tests don't require it, but feel free to update the <select> element to be a controlled element.

ItemForm

There is a new component called ItemForm that will allow us to add new items to our shopping list. When the form is submitted, a new item should be created and added to our list of items.

  • Make all the input fields for this form controlled inputs, so that you can access all the form data via state. When setting the initial state for the <select> tag, use an initial value of "Produce" (since that's the first option in the list).

  • Handle the form's submit event, and use the data that you have saved in state to create a new item object with the following properties:

    const newItem = {
  id: uuid(), // the `uuid` library can be used to generate a unique id
  name: itemName,
  category: itemCategory,
};

  • Add the new item to the list by updating state. To get the test passing, you'll need to use a prop called onItemFormSubmit as a callback and pass the new item to it.

    NOTE: to add a new element to an array in state, it's a good idea to use the spread operator:

    function addElement(element) {
  setArray([...array, element]);
}

    The spread operator allows us to copy all the old values of an array into a new array, and then add new elements as well. When you're working with state, it's important to pass a new array to the state setter function instead of mutating the original array.

Resources