page keeps giving Reload every time and Fetch function is executed

Question

const form = document.getElementById('form')
        form.addEventListener('submit', function (e) {
            e.preventDefault();

            const firsName = document.getElementById('firstname')
            const lastName = document.getElementById('lastName')
            const email = document.getElementById('email')
            const age = document.getElementById('age')
            const API_URL = 'http://localhost:3000/users';
            fetch(API_URL, {
                method: 'POST',
                body: JSON.stringify({
                    firsName,
                    lastName,
                    email,
                    age
                }),
                headers: {
                    "Content-Type": "application/json; charset=UTF-8"
                }
            }).then((response) =>response.json())
                .then((data) => {
                    console.log(data)
                })

        })