JSFiddle - React, Tailwind, and code Playground

HTML

<html>
        <head>
            <title>whatever</title>
            <script type="text/javascript">
                function myLittleTest() {
                    var obj, arr, armap, i;
    
                      // arr is an object and an array
                    arr = [1, 2, 3, 5, 7, 11];
    
                    obj = {}; // obj is only an object... not an array
                    alert (Object.prototype.toString.call(obj));

                    obj = arr; // obj is now an array and an object

                    alert (Object.prototype.toString.call(arr));
                    alert (Object.prototype.toString.call(obj));
                        // check for 

                    // works in IE
                    armap = [];
                    for(i = 0; i < obj.length; ++i)
                    {
                        armap.push(obj[i] * obj[i]);
                    }
                    alert (armap.join(", "));
    
                }
                // Changed from prueba();
                myLittleTest();
            </script>
        </head>
        <body>
        </body>
    </html>