@patternfly/react-core/src/helpers/useIsomorphicLayout.ts

This library provides a set of common React components for use with the PatternFly reference implementation.

import { useEffect, useLayoutEffect } from 'react';
import { canUseDOM } from './util';

/**
 * Small wrapper around `useLayoutEffect` to get rid of the warning on SSR envs
 */
export const useIsomorphicLayoutEffect = canUseDOM ? useLayoutEffect : useEffect;