res.send is not returning the expected data: JavaScript, Express, Node?

Question

I have a post request that submits a patient name and the server is supposed to give me back patient_id in response. I get a 200 response back to the client however I don't get the patient_id back which is what I need. When I console log on the server i can see patient.id is generated and there are no errors either. Wonder if there is something I am missing?

Response - 
body: (...), bodyUsed: false, headers: Headers {}, ok: true, redirected: false, status: 200, statusText: "OK", type: "basic", url: "http://localhost:4000/patient/add"

//client side post 

 handleSubmit(e) {
        e.preventDefault();
        const postUrl = '/patient/add';
        fetch(postUrl, {
            method: 'POST',
            headers: {'Content-Type': 'text/plain'},
            body: this.state.patientName
        })
            .then(response=> {
                if (!response.ok) console.log('failed', response);
                else console.log(response);
            });
    }

  this.app.post('/patient/add', bodyParser.text(),
            this.route_post_patient_add.bind(this));

 async route_post_patient_add(req, res) {
        /** @type {string} */
        const body = req.body;

        if (body === undefined) {
            logger.warning('Set room patient failed, body missing');
            res.sendStatus(400);
            return;
        }

        if (body === "") {
            logger.warning(' body is empty');
            res.sendStatus(400);
            return;
        }

        try { 
            const patient_id = await this.save_patient(body);

            res.send(patient_id);
            console.log(patient_id); //logs the id that is generated

        }
        catch (err) {
            logger.error('Set patient failed, internal error', { err });
            res.sendStatus(500);
        }
    }

Answer 1

The response object in fetch is not the raw body.

You have to call a function and resolve a promise to get the data.

For example:

fetch("foo")
    .then(parse_body)
    .then(log_data);

function parse_body(response) {
    return response.text();
}

function log_data(response_text) {
    console.log(response_text);
}

Further reading: MDN: Using Fetch