What problem does this feature solve?

https://github.com/vuejs/vue-next/blob/4a965802e883107a2af00301a59fb7f403b6acf7/packages/shared/src/index.ts#L104-L110 simplify code and remove any

What does the proposed API look like?

type strFunc = (str: string) => string
const cacheStringFunction = (fn: strFunc ): strFunc => {
  const cache: Record<string, string> = Object.create(null)
  return ((str: string) => {
    const hit = cache[str]
    return hit || (cache[str] = fn(str))
  }) 
}

Hi, thanks for your interest but Github issues are for bug reports and feature requests only. You can ask questions on the forum, the Discord server or StackOverflow.