JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 
                    "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
        <link rel="stylesheet" href="http://code.jquery.com/qunit/git/qunit.css" type="text/css" media="screen" />
    </head>
    <body>
        <h1 id="qunit-header">Testing isNumber using isNaN()</h1>
        <h2 id="qunit-banner"></h2>
        <div id="qunit-testrunner-toolbar"></div>
        <h2 id="qunit-userAgent"></h2>
        <ol id="qunit-tests"></ol>
        <div id="qunit-fixture">test markup, will be hidden</div>
        <script src="http://code.jquery.com/jquery-latest.js"></script>
        <script type="text/javascript" src="http://code.jquery.com/qunit/git/qunit.js"></script>  
    </body>
</html>

JavaScript

$(function () {
    var isNumber = function(val){
        return !isNaN( val );
    };
    test("test isNumber with numbers.", function () {
        equal(isNumber(10), true);
        equal(isNumber("123"),true);
    });
    test("test isNumber with non-numbers.", function () {
        equal(isNumber(true), false); // true converts to 1
        equal(isNumber(false), false); // false converts to 0
        equal(isNumber([]), false); // [] converts to 0
        equal(isNumber([2]), false); // [] converts to first element, which is 2.
        equal(isNumber(null), false); // null converst to 0
    });
});