Javascript 使用JQuery单击元素从新弹出窗口获取值

我的建议是将LI的点击侦听器移动到child.html，并使用Broadcast Channel API开始通信:

index.html

<button id="open-new-windows">TEST</button>

<script>
    const el = (sel, par = document) => par.querySelector(sel);

    el("#open-new-windows").addEventListener("click", (ev) => {
        window.open("http://localhost:3000/child.html", "TEST", "width=300,height=400");
    });

    const bc = new BroadcastChannel("comm");

    bc.addEventListener("message", (ev) => {
        // Do nothing if message is not from the expected origin:
        if ( ! /^http:\/\/localhost/.test(ev.origin)) return;
        // All OK: do something with the sent message:
        alert(ev.data);
    });
</script>

child.html

<ul>
    <li>This is LI 1</li>
    <li>This is LI 2</li>
    <li>This is LI 3</li>
    <li>This is LI 4</li>
    <li>This is LI 5</li>
    <li>This is LI 6</li>
    <li>This is LI 7</li>
</ul>

<script>
    const els = (sel, par = document) => par.querySelectorAll(sel);

    const bc = new BroadcastChannel("comm");

    const sendMessage = (ev) => {
        const elLI = ev.currentTarget;
        const text = elLI.textContent;
        bc.postMessage( text );
    };

    els("ul li").forEach(elLI => elLI.addEventListener("click", sendMessage) );
</script>

This way, even if you refresh the child.html page, it will attach again to the same broadcasting channel.
See here for another example

PS:
edit the above's http://localhost:3000/child.html to match your configuration.