function getAdvice() {
    // before fetching: show loader, hide quote el, disable btn
    loader.style.display = 'block';
    quoteEl.style.display = 'none';
    btn.disabled = true;

    fetch(url)
        .then(response => {
            return response.json();
        })
        .then(data => {
            // take id & advice from json
            let id = data.slip.id;
            let advice = data.slip.advice;
            
            // once fetched: hide loader, show quote el, make btn clickable
            loader.style.display = 'none';
            quoteEl.style.display = 'block';
            btn.disabled = false;

            // set id & advice into elements
            adviceId.innerHTML = id;
            quoteEl.innerHTML = advice;
        })
        .catch(function(error) {
            console.log(error);
        });
}