Finally, we have to define a proxy, to make sure that we can request our API from the same Uniform Resource Locator (URL) as the client. This is needed because, otherwise, we would have to deal with cross-site requests, which are a bit more complicated to handle. We are going to define a proxy that will forward requests from http://localhost:3000/api/ to http://localhost:4000/.

Now, let's configure the proxy:

1. First, we have to install the http-proxy-middleware package:

> npm install --save http-proxy-middleware

2. Then, we create a new src/setupProxy.js file, with the following contents:

const proxy = require('http-proxy-middleware')

module.exports = function (app) {
    app.use(proxy('/api', {

3. Next, we have to define the target of our proxy, which will be the backend server, running at http://localhost:4000:

        target: 'http://localhost:4000',

4. Finally, we have to define a path-rewrite rule, which removes the /api prefix before forwarding the request to our server:

        pathRewrite: { '^/api': '' }
    }))
}

The preceding proxy configuration will link /api to our backend server; therefore, we can now start both the server and the client via the following command:

> npm start

Then, we can access the API by opening http://localhost:3000/api/posts/react-hooks!