JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//ajax.googleapis.com/ajax/libs/jqueryui/1.10.4/jquery-ui.min.js"></script>
<link rel="stylesheet" href="//ajax.googleapis.com/ajax/libs/jqueryui/1.10.4/themes/smoothness/jquery-ui.css">
<ul id="completed-tasks">
    <li value="1">
        <label>item 1</label>
    </li>
    <li value="2">
        <label>item 2</label>
    </li>
    <li value="3">
        <label>item 3</label>
    </li>
</ul>

JavaScript

var totalValue = function () {
    //cycle over ul items
    var completedTasksHolder = document.getElementById("completed-tasks");
    var total = 0;
    for (var i = 0; i < completedTasksHolder.children.length; i++) {
        //I want to capture 'value' of each li here
        var v = parseInt(completedTasksHolder.children[i].getAttribute("value"));
        total += v;
    }
    //I want to add values here
    console.log(total);
}
totalValue();