JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-2.2.4.min.js"></script>
<h1>List</h1>
<ul id="list">

</ul>

JavaScript

var user = [{
    username: "alex", // use string
    age: 20
}, {
    username: "james", // use string
    age: 20
}]

function addUser(idx, user) {
    var username = user.username;
    var age = user.age

    var $user = $("<li>" + username + "</li>");
    var $age = $("<li>" + age + "</li>");

    $("#list").append($user).append($age); // use append for each node
}

$.each(user, addUser); // use function name instead of addUser()