您可以使用此函数作为参考，向接口添加回复。

let moreClass = document.querySelector("nav");
    sendBtn = document.querySelector(".sendBtn");
    comments = document.querySelector(".comments");
    let x =0;    
    console.log(sendBtn.getAttribute("value"))
    sendBtn.addEventListener("click",sendFunction)
    function sendFunction(){
            userTag = document.querySelector(".userTag").innerText;
            commentInput = document.querySelector(".commentInput");
            myValue= commentInput.value;
            const comment = document.createElement("div");
            comment.className="comment";
            comment.innerHTML=
                `<div class="commentUserPic">
                    <img width=100% src="../icons/profile_photo.png" alt="">
                </div>
                <div class="commentUserDesc">
                    <h2 class="commentUserName">${userTag}</h2>
                    <p class="commentContent">${myValue}</p>
                </div>`
            
            commentInput.value = "";
            comment.setAttribute("commentNumber",x);
            x++;
            comments.appendChild(comment);
            comments.scrollTop = comments.scrollHeight comments.clientHeight;
            
            
            
            })

希望能有所帮助。