script.js

function calculateTip(event) {
    event.preventDefault();
    let bill = document.getElementById('bill').value;
    let serviceQuality = document.getElementById('serviceQuality').value;
    let numOfPeople = document.getElementById('people').value; 

    if(bill < 0) {
        alert('O valor não pode ser negativo.');
        return;
    }

    if(numOfPeople < 1) {
        alert('Número de pessoas não pode ser negativo.');
        return;
    }
    if(numOfPeople == "") {
        numOfPeople = 1;
        document.getElementById('each').style.display = "none";
    }
    else {
        document.getElementById('each').style.display = "block";
    }

    let total = (bill * serviceQuality) / numOfPeople;
    total = total.toFixed(2);
    document.getElementById('tip').innerHTML = total;
    document.getElementById('totalTip').style.display = "block";
}

document.getElementById('totalTip').style.display = "none";document.getElementById('each').style.display = "none";

document.getElementById('tipsForm').addEventListener('submit', calculateTip);