Function crossfade

crossfade(
    __namedParameters: CrossfadeParams & {
        fallback?: (
            node: Element,
            params: CrossfadeParams,
            intro: boolean,
        ) => TransitionConfig;
    },
): [
    (
        node: any,
        params: CrossfadeParams & { key: any },
    ) => () => TransitionConfig,
    (
        node: any,
        params: CrossfadeParams & { key: any },
    ) => () => TransitionConfig,
]
The crossfade function creates a pair of transitions called send and receive. When an element is 'sent', it looks for a corresponding element being 'received', and generates a transition that transforms the element to its counterpart's position and fades it out. When an element is 'received', the reverse happens. If there is no counterpart, the fallback transition is used.

https://svelte.dev/docs/svelte-transition#crossfade
Parameters
- __namedParameters: CrossfadeParams & {
      fallback?: (
          node: Element,
          params: CrossfadeParams,
          intro: boolean,
      ) => TransitionConfig;
  }
Returns [
    (
        node: any,
        params: CrossfadeParams & { key: any },
    ) => () => TransitionConfig,
    (
        node: any,
        params: CrossfadeParams & { key: any },
    ) => () => TransitionConfig,
]