document.getElementbyId 未找到通过提取添加的元素

Question

我有一个聊天程序，可以在收到消息时向 dom 添加一个元素。此元素添加正确，但是当我从 dom 中查询它时，它显示为 null。我之前对服务器进行了一次获取，但它有一个 await 来减慢它的速度。有什么想法吗？

这是我的 javascript 代码

        socket.on('receive_message', async function(data) {
            let messaged_user_li = document.getElementById('messaged_user_li'+data['from_user']);
            console.log('messaged_user_li: '+messaged_user_li)
            if (messaged_user_li == null) {
                console.log('if fired')
                await fetch('/get_messaged_user/'+data['from_user']).then((response) => {
                    response.json().then((data2) => {
                        loadMessagedUser(data2[0].id, data2[0].avatar, data2[0].username, data2[0].last_seen);
                    });
                });
                console.log(data['from_user'])
                messaged_user_li = document.getElementById('messaged_user_li'+data['from_user']);
                //despite this element being added this log shows nulls which causes issues later on in the code.
                console.log('messaged_user_li: '+messaged_user_li)     
            }
            
            let message_user = document.getElementById('message_user'+data['from_user']);

            let message_target = document.getElementById("message_target"+data['from_user']);
            if (messaged_user_li.classList.contains('active') == false) {
                messaged_user_li.classList.add('flash-message');
            }
            if (message_user != null) {
                data = `
                <li class="clearfix">
                    <div class="message-data text-right">
                        <span class="message-data-time">just now</span>
                    </div>
                    <div class="message other-message float-right">`+data['message']+`</div>
                </li>`;
                message_target.innerHTML += data;
                //Move scroller to bottom when message received
                myDiv = message_user.querySelector(".chat-history");
                myDiv.scrollTop = myDiv.scrollHeight;
            }
        });

Answer 1

您只需要等待此承诺完成：

await fetch('/get_messaged_user/'+data['from_user']).then((response) => {
    // ...
});

回调中没有这个：

response.json().then((data2) => {
    loadMessagedUser(data2[0].id, data2[0].avatar, data2[0].username, data2[0].last_seen);
});

这就是为什么您的代码继续执行并尝试获取添加的元素（尚未添加）的原因。

要解决此问题，您可以链接 then 调用：

await fetch('/get_messaged_user/'+data['from_user'])
    .then((response) => response.json())
    .then((data2) => loadMessagedUser(data2[0].id, data2[0].avatar, data2[0].username, data2[0].last_seen));

或再次使用await：

const response = await fetch('/get_messaged_user/'+data['from_user']);
const data2 = await response.json();
loadMessagedUser(data2[0].id, data2[0].avatar, data2[0].username, data2[0].last_seen);

document.getElementbyId 未找到通过提取添加的元素

document.getElementbyId is not finding element added by a fetch

javascript

async-await

fetch

getelementbyid