react-spring/packages/core/src/hooks/useSpring.ts

import { Lookup, Remap } from '@react-spring/types'
import { is } from '@react-spring/shared'

import { ControllerUpdate, PickAnimated, SpringValues } from '../types'
import { Valid } from '../types/common'
import { SpringRef } from '../SpringRef'
import { useSprings } from './useSprings'

/**
 * The props that `useSpring` recognizes.
 */
export type UseSpringProps<Props extends object = any> = unknown &
  PickAnimated<Props> extends infer State
  ? State extends Lookup
    ? Remap<
        ControllerUpdate<State> & {
          /**
           * Used to access the imperative API.
           *
           * When defined, the render animation won't auto-start.
           */
          ref?: SpringRef<State>
        }
      >
    : never
  : never

/**
 * The `props` function is only called on the first render, unless
 * `deps` change (when defined). State is inferred from forward props.
 */
export function useSpring<Props extends object>(
  props:
    | Function
    | (() => (Props & Valid<Props, UseSpringProps<Props>>) | UseSpringProps),
  deps?: readonly any[] | undefined
): PickAnimated<Props> extends infer State
  ? State extends Lookup
    ? [SpringValues<State>, SpringRef<State>]
    : never
  : never

/**
 * Updated on every render, with state inferred from forward props.
 */
export function useSpring<Props extends object>(
  props: (Props & Valid<Props, UseSpringProps<Props>>) | UseSpringProps
): SpringValues<PickAnimated<Props>>

/**
 * Updated only when `deps` change, with state inferred from forward props.
 */
export function useSpring<Props extends object>(
  props: (Props & Valid<Props, UseSpringProps<Props>>) | UseSpringProps,
  deps: readonly any[] | undefined
): PickAnimated<Props> extends infer State
  ? State extends Lookup
    ? [SpringValues<State>, SpringRef<State>]
    : never
  : never

/** @internal */
export function useSpring(props: any, deps?: readonly any[]) {
  const isFn = is.fun(props)
  const [[values], ref] = useSprings(
    1,
    isFn ? props : [props],
    isFn ? deps || [] : deps
  )
  return isFn || arguments.length == 2 ? [values, ref] : values
}