var url = 'http://localhost:8000/employees/';

fetch (url,{
    method: "post",
    body: JSON.stringify({
        id: 5,
        fullname: 'Táncos Imre',
        city: "Szeged",
        salary: 2250000
    }),
    headers: {
        "Content-Type": "application/json"
    }
})
.then(response => response.json())
.then(result => {
    console.log(result);
}).catch(err => {
    console.log(err);
});