如何将$ ajax转换为fetch

I am trying to use Fetch in my React component, but I am not sure that I understand well the syntax. Currently I am using Ajax with jQuery:

handleDeleteProject(projectID) {
    $.ajax({
        url: './comments/delete',
        data: { productID: projectID },
        type: 'get',
        cache: true,
        success: function (response) {
            console.log("ok");
        },
    });
}

And I want to convert it to Fetch. Right now I have somethinkg like that, but it does not work. Event does not go through breakpoint in server's controller:

fetch('./comments/delete', {
        method: 'get',
        body: "productID=" + encodeURIComponent(projectID)
    })
        .then(res => res.json())
        .then(res => {
            console.log('usunąłęm produkt:');
            console.log(res);
        })

You don't want to send the productID in the body of the request, but as a query parameter. You also don't have to specify the method, since GET is the default.

fetch("/comments/delete?productID=" + encodeURIComponent(projectID))
  .then(res => res.json())
  .then(res => {
    console.log(res);
  })
  .catch(error => {
    console.error(error);
  });

Off topic: You most likely don't want to delete resources with a GET request. Look into changing it to a DELETE request instead.