Targets

What is a target?

When a target is discussed it is sometimes in reference to the platform, e.g. you create a client side react application changes are it's targetted at the browser. However, if you write a server-side application then you're targetting node. Whilst react-spring does support the targets web and native and can be server-side rendered. This is not the type of target we're referring too.

A target in react-spring is a react reconciler a.k.a react renderer. That is, a custom renderer that can process different JSX components, it's duty is to create / update and remove these elements from the browser. react-dom is a prime example of a reconciler, it handles DOM elements exclusively and understands how to apply attributes to those DOM nodes via react props.

Therefore, in react-spring we have the following targets that correspond to their respective reconcilers:

• web - react-dom
• native - react-native
• three - react-three-fiber
• konva - react-konva
• zdog - react-zdog

To download a target you can use the @react-spring/[target] format:

yarn add @react-spring/web

Adding a target

To create your own target, we offer the createHost function. This function returns the animated components related to the specific target, e.g. the host created in @react-spring/web returns the animated dom components such as animated.div.

The signature for createHost function looks like this:

type CreateHost = (
  components: AnimatableComponent[] | { [key: string]: AnimatableComponent },
  config: Partial<HostConfig>
) => {
  animated: WithAnimated
}

AnimatableComponent

The first argument AnimatableComponent[] | { [key: string]: AnimatableComponent }, is a list of strings that relate the native elements of the renderer you're targeting. Using the same example of @react-spring/web, the components would include the strings 'div', 'li' etc. These components are then created into Animated components in the createHost function via the withAnimated HOC.

HostConfig

interface HostConfig {
  /** Provide custom logic for native updates */
  applyAnimatedValues: (node: any, props: Lookup) => boolean | void
  /** Wrap the `style` prop with an animated node */
  createAnimatedStyle: (style: Lookup) => Animated
  /** Intercept props before they're passed to an animated component */
  getComponentProps: (props: Lookup) => typeof props
}

Whilst the entire config object is wrapped in Partial, meaning that the keys are optional, realistically applyAnimatedValues is required. This is the logic for how the Animated components apply their SpringValues, this typically would come from the reconciler either attached to the instance in the case of react-konva or an exported function like in @react-three/fiber.

The createAnimatedStyle key of the config object by default takes wraps the style prop in an AnimatedObject instance which has generic rules on applying keys. In the case of @react-spring/web, we pass a custom function which is how we support shorthands for transformation styles.

The getComponentProps is a middeleware function that allows you to intercept props before they're passed to the animated component, therefore you could omit props e.g. scrollTop for the web because @react-spring/web expects this to be in the style object.

For more information on animated elements, see here.