I struggle with correct syntax on fetching an API while adding to the request the document.URL.

My request looks like this:

function fetchApi() {
    return fetch('https://api.sistrix.com/domain.sichtbarkeitsindex?api_key=myKey&domain=example.com&format=json')
    .then(response => {
        if (!response.ok) {
            return response.text().then(text => {throw new Error(text)});
        }                
        return response.text();
    })

}

return fetchApi()
    .then(intent => seoSpider.data(intent))
    .catch(error => seoSpider.error(error));

It works, like expected. Now I want to replace ‘example.com’ with ‘document.URL’ – but have no success with correct syntax.

I tried it with return fetch('https://api.sistrix.com/domain.sichtbarkeitsindex?api_key=myKey&format=json&domain' + document.URL) – but it doesn’t work, API doesn’t recognize document.URL as valid address.