cacheNext.js

let cache = {};

class App extends React.Component {
  static async getInitialProps({ req, query, asPath, pathname }) {

    let data;
    //if data is in cache then use the cache
    if (cache[someID]) {
      data = cache[someID]
    } else {
      //if not, then fetch from server
      data = await fetch(`someAPI`);
    }
  
    return { data }
    
  }

  render() {
      //check if client, if so store the data in the cache. 
      //If you don't do this check, there will be a separate cache stored on the server since Next.js does server side rendering as well.
      if (process.browser) {
        cache[someID] = this.props.data;
      }
    
      return (
      <div></div>
      )
    }
  }

export default App;