每次我点击提交按钮，数据被添加到JSON服务器，但是页面被刷新，我不希望发生这种情况。为什么防止默认值不起作用？我怎样才能防止页面刷新？

let form = document.getElementById("addBooksForm").addEventListener("submit",getBooksData);
let tbody = document.getElementById("tbody");

let bookDetails = {};

function getBooksData(event){
    
    event.preventDefault()
    
    let coverUrl = document.getElementById("url").value;
    let name = document.getElementById("name").value;
    let author = document.getElementById("author").value;
    let genre = document.getElementById("genre").value;
    let edition = document.getElementById("edition").value;
    let publisher = document.getElementById("publisher").value;
    let price = document.getElementById("price").value;
    
    bookDetails = {
        coverUrl,
        name,
        author,
        genre,
        edition,
        publisher,
        price,
        borrowed: false
    };

    
    addBooks(bookDetails);
    fetchBooks();
}

async function addBooks(bookDetails){

     try{
        let res = await fetch(`http://localhost:8080/books`,{
            method: "POST",
            body: JSON.stringify(bookDetails),
            headers: {"Content-Type":"application/json"}
        });
        let data = await res.json();
        console.log(data)
     }catch(err){

     }
}