How to concatenate HREF to get id from database?

NodeJS, Mongoose

<% for(var i = 0; i < articles.length; i++){ %>
  <ul class="list-group">
    <li class="list-group-item">
      <a href="/article/<%=articles._id%>">
        <%= articles[i].title %>
      </a>
    </li>
  </ul>
<% } %>
<% include partials/html-footer %>

How do I make it go to /articles/articles._id? I've tried -

<a href="/article/"+<%=articles._id%>>

as well. If there's anything else you need to see, let me know. Don't know what else to post.