How do I send a variable from Express.js backend to React.js frontend?

I am trying to send my variable ‘backEndResponse’ with its value from my Express.js backend to my React.js Frontend. I am not quite sure how to send a variable from the backend to the frontend. I have searched around and can’t find any good resources. I would appreciate any help.

Express.js Backend

 function getcookie(req) {
        var authCookie = req.headers.cookie;
        try{
        return authCookie
            .split('; ')
            .find(row => row.startsWith('Auth='))
            .split('=')[1];
        } finally {
            if (authCookie = result) {
                backEndResponse = true
                console.log(backEndResponse);
                console.log(result);
            } else {
                backEndResponse = false
                console.log(backEndResponse);
                console.log(result);
            }
        }
    }
    
    app.get('/auth', (req, res) => {
        backEndResponse
    });

Frontend React.js

let backEndResponse = null

axios.get('http://localhost:5000/auth', { withCredentials: true }).then((res) => {
        // backEndResponse
    })

const useAuth = () => {
    if (backEndResponse) {
        const authorized = {loggedIn: true}
        return authorized && authorized.loggedIn;
    } else {
        const authorized = {loggedIn: false}
        return authorized && authorized.loggedIn;
    }
};