In the typical React dataflow, props are the only way that parent components interact with their children. To modify a child, you re-render it with new props. However, there are a few cases where you need to imperatively modify a child outside of the typical dataflow. The child to be modified could be an instance of a React component, or it could be a DOM element. For both of these cases, React provides an escape hatch.
When to Use Refs
There are a few good use cases for refs:
- Managing focus, text selection, or media playback.
- Triggering imperative animations.
- Integrating with third-party DOM libraries.
Avoid using refs for anything that can be done declaratively.
For example, instead of exposing open() and close() methods on a Dialog component, pass an isOpen prop to it.
Don’t Overuse Refs
Your first inclination may be to use refs to “make things happen” in your app. If this is the case, take a moment and think more critically about where state should be owned in the component hierarchy. Often, it becomes clear that the proper place to “own” that state is at a higher level in the hierarchy. See the Lifting State Up guide for examples of this.
Creating Refs
Refs are created using React.createRef() and attached to React elements via the ref attribute. Refs are commonly assigned to an instance property when a component is constructed so they can be referenced throughout the component.
Accessing Refs
When a ref is passed to an element in render, a reference to the node becomes accessible at the current attribute of the ref.
The value of the ref differs depending on the type of the node:
- When the
refattribute is used on an HTML element, therefcreated in the constructor withReact.createRef()receives the underlying DOM element as itscurrentproperty. - When the
refattribute is used on a custom class component, therefobject receives the mounted instance of the component as itscurrent. - You may not use the
refattribute on function components because they don’t have instances.
The examples below demonstrate the differences.
Exposing DOM Refs to Parent Components
In rare cases, you might want to have access to a child’s DOM node from a parent component. This is generally not recommended because it breaks component encapsulation, but it can occasionally be useful for triggering focus or measuring the size or position of a child DOM node.
While you could add a ref to the child component, this is not an ideal solution, as you would only get a component instance rather than a DOM node. Additionally, this wouldn’t work with function components.
If you use React 16.3 or higher, we recommend to use ref forwarding for these cases. Ref forwarding lets components opt into exposing any child component’s ref as their own. You can find a detailed example of how to expose a child’s DOM node to a parent component in the ref forwarding documentation.
If you use React 16.2 or lower, or if you need more flexibility than provided by ref forwarding, you can use this alternative approach and explicitly pass a ref as a differently named prop.
When possible, we advise against exposing DOM nodes, but it can be a useful escape hatch. Note that this approach requires you to add some code to the child component. If you have absolutely no control over the child component implementation, your last option is to use findDOMNode(), but it is discouraged and deprecated in StrictMode.
If you are just starting to program, you may need some help. You can find it here https://itmaster-soft.com/en/react-native-development-services