framer-motion/src/utils/use-constant.ts

An open source and production-ready motion library for React on the web

import { useRef } from "react"

type Init<T> = () => T

/**
 * Creates a constant value over the lifecycle of a component.
 *
 * Even if `useMemo` is provided an empty array as its final argument, it doesn't offer
 * a guarantee that it won't re-run for performance reasons later on. By using `useConstant`
 * you can ensure that initialisers don't execute twice or more.
 */
export function useConstant<T>(init: Init<T>) {
    const ref = useRef<T | null>(null)

    if (ref.current === null) {
        ref.current = init()
    }

    return ref.current
}