How to use the @cubejs-client/core function in @cubejs-client/core

cubejsApi() {
    const { cubejsToken, apiUrl } = this.state;
    if (!this.cubejsApiInstance && cubejsToken) {
      this.cubejsApiInstance = cubejs(cubejsToken, {
        apiUrl: `${apiUrl}/cubejs-api/v1`
      });
    }
    return this.cubejsApiInstance;
  }

import React, { Component } from 'react';
import { Container, Row, Col } from 'reactstrap';
import { AreaChart, Area, XAxis, YAxis, Tooltip, ResponsiveContainer, PieChart, Pie, Cell, Legend, BarChart, Bar } from 'recharts';
import moment from 'moment';
import numeral from 'numeral';
import cubejs from '@cubejs-client/core';
import Chart from './Chart.js';
import GithubCorner from 'react-github-corner';

const cubejsApi = cubejs(process.env.REACT_APP_CUBEJS_TOKEN);
const currencyFormatter = (item) => numeral(item).format('$0,0')
const dateFormatter = (item) => moment(item).format('MMM YY')

class App extends Component {
  render() {
    return (

import React, { useEffect } from "react";
import "./App.css";
import { Layout } from "antd";
import cubejs from "@cubejs-client/core";
import { CubeProvider } from "@cubejs-client/react";
import Header from "./components/Header";
import WebSocketTransport from "@cubejs-client/ws-transport";
import tracker from "./tracker";
const CUBEJS_TOKEN = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpYXQiOjE1NzM2MjI5MjR9.iD_sSpXRBQSO0ywh5zSPHpHV-1O37oQMakrkG03kR-o";
let WS_URL;
if (process.env.NODE_ENV === 'production') {
  WS_URL = window.location.origin.replace('http', 'ws').replace('https', 'wss')
} else {
  WS_URL = "ws://localhost:4000/"
}
const cubejsApi = cubejs({
  transport: new WebSocketTransport({
    authorization: CUBEJS_TOKEN,
    apiUrl: WS_URL
  })
});

const AppLayout = ({ children }) => (
  
    <header>
    {children}
  
);</header>

Area,
  XAxis,
  YAxis,
  Tooltip,
  ResponsiveContainer,
  Legend,
  BarChart,
  Bar
} from "recharts";
import moment from "moment";
import numeral from "numeral";
import cubejs from "@cubejs-client/core";
import Chart from "./Chart.js";
import GithubCorner from 'react-github-corner';

const cubejsApi = cubejs(process.env.REACT_APP_CUBEJS_TOKEN, {
  apiUrl: process.env.REACT_APP_API_URL
});
const numberFormatter = item => numeral(item).format("0,0");
const dateFormatter = item => moment(item).format("MMM YY");

const renderSingleValue = (resultSet, key) => (
  <h1 height="{300}">{numberFormatter(resultSet.chartPivot()[0][key])}</h1>
);

class App extends Component {
  render() {
    return (

(
                      resultSet && renderChart(resultSet) || ()
                    )}
                  />

import './body.css';
import 'antd/dist/antd.css';
import React from "react";
import { ApolloProvider } from '@apollo/react-hooks';
import { Layout } from "antd";
import cubejs from '@cubejs-client/core';
import { CubeProvider } from "@cubejs-client/react";
import client from "./graphql/client";
import Header from "./components/Header";

const API_URL = undefined;

const CUBEJS_TOKEN = undefined;

const cubejsApi = cubejs(
  CUBEJS_TOKEN,
  { apiUrl: `${API_URL}/cubejs-api/v1` }
);

const AppLayout = ({ children }) => (
  
    <header>
    {children}
  
);

const App = ({ children }) =&gt; (</header>

render() {
    const cubejsApi = cubejs('eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpIjo0MDEzN30.8Slfo_q1LUFAflOoLksmtNxT0MnrwKkf3SX1N6d77Rw');
    return (
      
        <h1>React E-Commerce Dashboard built with Cube.js</h1>

cubejsApi() {
    const { cubejsToken, apiUrl } = this.state;
    if (!this.cubejsApiInstance && cubejsToken) {
      this.cubejsApiInstance = cubejs(cubejsToken, {
        apiUrl: `${apiUrl}/cubejs-api/v1`
      });
    }
    return this.cubejsApiInstance;
  }

import './body.css';
import 'antd/dist/antd.css';
import React from "react";
import { Layout } from "antd";
import cubejs from '@cubejs-client/core';
import { CubeProvider } from "@cubejs-client/react";
import Header from "./components/Header";

const API_URL = undefined;

const CUBEJS_TOKEN = undefined;

const cubejsApi = cubejs(
  CUBEJS_TOKEN,
  { apiUrl: `${API_URL}/cubejs-api/v1` }
);

const AppLayout = ({ children }) => (
  
    <header>
    {children}
  
);

const App = ({ children }) =&gt; (</header>