Question

以下JS位于HTML下方的脚本标签中。最初加载页面时，该文件似乎可以工作。创建一个通道后，当我单击该通道时，会出现console.log语句，表明该通道正在运行。然后，我成功添加频道。但是，当我单击其他频道时，什么也没有发生。我从未到达页面底部的.forEach和click eventListener －一种专门为多个通道按钮构建的案例。我尝试了各种配置，并研究了查询选择器和forEach。我要去哪里错了？

(function() {


    //connect to websocket: copy must be inside request.onload for chat room to register user entry
    let socket = io.connect(location.protocol + '//' + document.domain + ':' + location.port);

    if (socket) 
        console.log("Socket connected!");

    socket.on('connect', () => {
        // track number of channels and channel names
        let channelCount = 1;
        let channelList = ["Lobby"];

        // create & display new channels added by user
        let createChannelBtn = document.querySelector('#chanlBtn');

        createChannelBtn.addEventListener('click', function(e) {

            //e.preventDefault();

            let newChannel = document.querySelector('#chanl').value;

            // add a channel if not a duplicate
            if (channelList.indexOf(newChannel) > -1) {

                document.querySelector('#chanl').value = '';

            } else {
                channelCount += 1;
                channelList.push(newChannel);

                console.log(channelList);
                console.log(channelCount);
                let textnode = document.createTextNode(newChannel);
                let node = document.createElement('button');
                node.className += 'dropdown-item';
                node.setAttribute('type', 'button');
                node.setAttribute('id', 'selectChannel');
                node.setAttribute('data-channel-', 'newChannel');
                node.appendChild(textnode);
                document.querySelector('#chanlMenu').appendChild(node);
                document.querySelector('#chanl').value = '';

            }

        });

        if (channelCount == 1) {
            var channel_button = document.querySelector('#selectChannel');
            console.log("channel 1 =" + channel_buttons);
            console.log("channelCount 1 =" + channelCount);
            channel_button.addEventListener('click', function() {
                let room = channel_button.dataset.channel;
                console.log("Inside lobby");
                socket.emit('join', {'username':localStorage.getItem('login'), 'room':room});
            });
        } 

        var channel_buttons = document.querySelectorAll('#selectChannel');


    HERE'S THE SECTION I NEVER REACH AFTER A CHANNEL BUTTON IS ADDED
            channel_buttons.forEach( channel_button => {
                channel_button.addEventListener('click', function() {
                let room = channel_button.dataset.channel;
                console.log("Sending 1 Button signal from Node List");
                //socket.emit('join', {'username':localStorage.getItem('login'), 'room':room});
            });

        });

    });

})()

Answer 1

页面加载时，您似乎将点击处理程序添加到了通道按钮。

此问题是按钮尚不存在，因此您正在遍历var channel_buttons = document.querySelectorAll('#selectChannel');

创建的空列表

（尝试在该行之后放置console.log(channel_buttons);，以查看列表中包含的内容）

您需要将事件侦听器添加到已创建的节点上（可能在node.addEventListener(...)行之后添加node.appendChild(textnode);，或使用event delegation在其上放置点击处理程序）父级将处理所有新按钮的点击。

读过一次Javascript会被部分忽略吗？

1 个答案: