Compound components in React allow you to create components with some form of connected state that’s managed amongst themselves. A good example is the Form component in Semantic UI React.
To see how we can implement compound components in a real-life React application, we’ll build a compound (multi-part) form for login and sign up. The state will be saved in the form component and we’ll put React’s Context AP to use to pass that state and the method from the Context Provider to the component that needs them. The component that needs them? It will become a subscriber to Context Consumers.
Here’s a rough outline that shows how the following steps fit together:
Before treading any further, you may want to brush up on the React Context API if you haven’t already. Neal Fennimore demonstrates the concept in this post and my primer on it is worth checking out as well.
Step 1: Creating context
First, let’s initialize a new context using the React Context API.
The provider, FormProvider, will hold the application state, making it available to components that subscribe to FormConsumer.
Step 2: Implement provider
One panel contains the form to log in and the other contains the form to sign up. In the provider, we want to declare the state, which determines the active panel, i.e. the form currently in display. We’ll also create a method to switch from one panel to another when a heading is clicked.
By default, the login panel will be shown to the user. When the signup panel is clicked, we want to make it the active panel by setting the state of activePanel to signup using the method handlePanelSwitch().
Step 3: Implement Consumers
We’ll use FormConsumer to make context available to the components that subscribe to it. That means the FormPanel component that handles displaying panels will look like this:
To understand what is happening, let’s understand the approach here. The login and signup panels will have unique IDs that get passed via props to the Panel component. When a panel is selected, we get the ID and and use it to set activePanel to swap forms. The FormPanel component also receives the name of the panel via the isActive prop and we then check to see if the returned value is true. If it is, then the panel is rendered!
To get the full context, here is how the App component looks: