Json Web token and implementation in front end & sever side?

Question

I want to know about Json web token and how to implement.
If we use **node.js** as backend with the help of express js and **react** as front end, what will be the code for **Jwt**. Please explain with example.

please see my code but not working

app.post('/signin', async(req, res)=>{
            const user = req.body;
            const accessToken = jwt.sign(user,process.env.ACCESS_TOKEN_SECRET,{
                ExpireIn: '1d'
            })
            res.send({accessToken})

;