`as` polymorphism in React 19

polymorphism.ts

import React, { JSX } from 'react'

type IntrinsicElements = keyof JSX.IntrinsicElements

// Intrinsic elements e.g. 'div'
type IntrinsicElementProps<Element extends IntrinsicElements> = {
  as?: Element
} & React.ComponentPropsWithRef<Element>

// Custom React components e.g. next/link
type CustomElementProps<Element extends React.ElementType> = {
  as?: any
  ref?: React.Ref<React.ComponentRef<Element>>
} & React.ComponentPropsWithoutRef<Element>

export type PolyProps<Element, CustomProps> = Element extends IntrinsicElements
  ? IntrinsicElementProps<Element> & CustomProps
  : Element extends React.ElementType
    ? CustomElementProps<Element> & CustomProps
    : never