未捕获的类型错误：无法读取 node.js 上未定义的属性“长度”

Question

How's it going?

I have been trying to put some upvotes functionalities on this web app I have been developing but I am stuck. Please help. The error that it is shown on Chrome's console is:

Uncaught TypeError: Cannot read property 'length' of undefined at createUpvotesSection ((index):41) at XMLHttpRequest.ajax.onreadystatechange ((index):343)

But could it be? I have already stated the "createUpvotesSection" and tried to use it in Index.ejs as you can see below:

Index.ejs:

function showNewsfeed() {
    var ajax = new XMLHttpRequest();
    ajax.open("POST", "/getNewsfeed", true);

    ajax.onreadystatechange = function() {
        if (this.readyState == 4 && this.status == 200) {

            var response = JSON.parse(this.responseText);

            var html = "";
            for (var a = 0; a < response.data.length; a++) {
                var data = response.data[a];

                html += '<div class="central-meta item">';
                    html += '<div class="user-post">';
                        html += '<div class="friend-info">';

                            html += '<figure>';
                                html += '<img src="' + mainURL + "/" + data.user.profileImage + '" style="width: 45px; height: 45px; object-fit: cover;">';
                            html += '</figure>';

                            html += '<div class="friend-name">';
                                html += '<ins>';
                                    if (data.type == "post")
                                    {
                                        html += '<a href="/user/' + data.user.username + '">';
                                            html += data.user.username;
                                        html += '</a>';
                                    }
                                    else
                                    {
                                        html += data.user.name;
                                    }
                                html += '</ins>';

                                var createdAt = new Date(data.createdAt);
                                var date = createdAt.getDate() + "";
                                date = date.padStart(2, "0") + " de " + months[createdAt.getMonth()] + ", " + createdAt.getFullYear();

                                html += '<span>Publicado em: ' + date + '</span>';
                            html += '</div>';

                            html += '<div class="post-meta">';

                                html += '<div class="description">';
                                    html += '<p>';
                                        html += data.caption;
                                    html += '</p>';
                                html += '</div>';

                                if (data.image != "") {
                                    html += '<img src="' + mainURL + "/" + data.image + '">';
                                }

                                if (data.video != "") {
                                    html += '<video style="height: 359px; width: 100%;" controls src="' + mainURL + "/" + data.video + '"></video>';
                                }
                            
                                html += createUpvotesSection(data);
                            html += '</div>';
                        html += '</div>'
                    html += '</div>';
                html += '</div>';
            }
            document.getElementById("newsfeed").innerHTML = html;
        }
    };

Header.ejs (shorter version):

function createUpvotesSection(data) {

                var isUpvoted = false;
                for (var b = 0; b < data.upvoters.length; b++) {
                    var upvoter = data.upvoter[b];
                    if (upvoter._id == window.user._id) {
                        isUpvoted = true;
                        break;
                    }
                }

                var html = "";

                html += '<div class="we-video-info">';
                    html += '<ul>';

                        html += '<li>';
                            var className = "";
                            if (isUpvoted) {
                                className = 'upvote';
                            } else {
                                className = "none";
                            }

                            html += '<span class="' + className +'" onclick="toggleUpvotePost(this);" data-id="' + data._id +'">';
                                html += '<i class="ti-thumb-up"></i>';
                                html += '<ins>' + data.upvoters.length + '</ins>';
                            html += '</span>';

                        html += '</li>';

                        html += '<li>';
                            html += '<span class="comment" title="Comments">';
                                html += '<i class = "fa fa-comments-o"></i>';
                                html += '<ins>' + data.comments.length + '</ins>';
                            html += '</span>';
                        html += '</li>';

                        html += '<li>';
                            html += '<span class="share" onclick="sharePost(this);" data-id="' + data._id +'">';
                                html += '<i class="ti-share"></i>';
                                html += '<ins>' + data.shares.length + '</ins>';
                            html += '</span>';
                        html +=  '</li>';

                    html += '</ul>';
                html += '</div>';

                return html;
            }

Answer 1

According to the error that Cannot read property 'length' of undefined on node.js that means the variable that you try to get length of it is undefined variable. try to define that first before you take the length