JSFiddle - React, Tailwind, and code Playground

HTML

<textarea class="comment-text" cols="30" rows="10" placeholder="enter your comment"></textarea>
<button class="btn-post">post</button>
<ul class="posts">
    
</ul>

CSS

.disabled {
    cursor: not-allowed;
    pointer-events: none;
    opacity: 0.65;
}

JavaScript

$(".comment-text").keydown(function (e) {
        if (e.which === 13) {
            $("this.form").submit();
            return false;
        }
    });

    $('.comment-text').keydown(function (event) {
        var post = $(".comment-text").val();
        if (event.which === 13) {
            $("<li>").text(post).appendTo(".posts");
            $(".comment-text").val("");
        }
    });

      /*#############Disable enter when there is no text##############*/
    $(".comment-text").keydown(function(e) {
        var post = $(".comment-text").val();
        if (e.which === 13 && e.target.value === ""){
            e.preventDefault();
            e.cancelBubble = true;
        console.log(e);}}, true);

    $(".comment-text").keydown(function(e){
        if(e.which === 13)console.log($("<li>").text(post).appendTo(".posts")); });
    
    /*##################################################*/

    $(".btn-post").click(function () {
        var post = $(".comment-text").val();
        $("<li>").text(post).appendTo(".posts");
        $(".comment-text").val("");
        $(".btn-post").addClass("disabled");
    });

    $(".comment-text").keyup(function () { /*disable button when there is no text in comment-text */
        var postlength = $(".comment-text").val().length;
        if (postlength === 0) {
            $(".btn-post").addClass("disabled");
        } else if (postlength <= 0) {
            $(".btn-post").addClass("disabled");
        } else {
            $(".btn-post").removeClass("disabled");
        }
    });

    $(".btn-post").addClass("disabled");