JSFiddle - React, Tailwind, and code Playground

HTML

AARRGGBB Color to aRGB Converter<br />
<small>Accepts #AARRGGBB #RRGGBB #RGB formats, with or without the # symbol.</small>
<br /><br />
<input id="hexinput" type='text' />
<br />
<h1 id="results"></h1>

JavaScript

function hexToRgba(hex) {
    var bigint, r, g, b, a;
    //Remove # character
    var re = /^#?/;
    var aRgb = hex.replace(re, '');
    if (aRgb.length == 3) {
        bigint = parseInt(aRgb, 16);
        r = (bigint >> 4) & 255;
        g = (bigint >> 2) & 255;
        b = bigint & 255;
        return "rgba(" + r + "," + g + "," + b + ",1)";
    }
    if (aRgb.length == 6) {
        bigint = parseInt(aRgb, 16);
        r = (bigint >> 16) & 255;
        g = (bigint >> 8) & 255;
        b = bigint & 255;
        return "rgba(" + r + "," + g + "," + b + ",1)";
    }
    if (aRgb.length == 8) {
        bigint = parseInt(aRgb, 16);
        a = ((bigint >> 24) & 255) / 255;
        r = (bigint >> 16) & 255;
        g = (bigint >> 8) & 255;
        b = bigint & 255;
        return "rgba(" + r + "," + g + "," + b + "," + a.toFixed(1) + ")";
}

}

$('#hexinput').on('input', function () {
    $('#results').text(hexToRgba($('#hexinput').val()));
});
$('#myTextbox1').on('input', function () {
    alert('Text1 changed!');
});