app.js

var h = new Headers()
h.append('Authorization', 'Bearer xxx');
h.append('Cookie', 'xxx');
h.append('Content-Type', 'application/json');
fetch('http://localhost:4567/api/reviews', {
    headers: h,
    method: 'POST',
    body: JSON.stringify({ "foo": "bar" })
}).then(function (res) {
    return res.json().then(function (json) {
        console.log(json)
    });
});