Get query string value in React JS

Probably the best way is to use the useParams hook because you have a functional component. Read from the documentation as the following:

useParams returns an object of key/value pairs of URL parameters. Use it to access match.params of the current <Route>.

I would suggest the following:

import React from 'react'
import { useParams } from 'react-router-dom'

const Callback = () => {
   let { code } = useParams()

   console.log({ code });

   return (
      <React.Fragment>
          Callback
      </React.Fragment>
   )
};

+1 from documentation:

You need to be using React >= 16.8 in order to use any of these hooks!

use this library 'query-string' and use as

import queryString from 'query-string';

in constructor

  constructor(props) {
    const { location: { search } } = props;
    const parsed = queryString.parse(search);
     this.state = {
      code: parsed.code,
       }
   }

hope it will solve your problem !