JSFiddle - React, Tailwind, and code Playground

HTML

<html>
    <head>
        <script type="text/javascript">
            function format(input)
            {
                var nStr = input.value + '';
                nStr = nStr.replace( /\,/g, "");
                x = nStr.split( '.' );
                x1 = x[0];
                x2 = x.length > 1 ? '.' + x[1] : '';
                var rgx = /(\d+)(\d{3})/;
                while ( rgx.test(x1) ) {
                    x1 = x1.replace( rgx, '$1' + ',' + '$2' );
                }
                input.value = x1 + x2;
            }
        </script>
    </head>
    <body>
        <input type="text" onkeyup="format(this)">
    </body>
</html>