Untitled

(function(d) {
    d.open();
    d.write('<textarea id="input" spellcheck="false" style="flex:1;height:100%;resize:none;outline:none;font:15px monospace;color:#fff;background:#111;padding:10px;"><html>\n<head></head>\n<body>\nClick here to render\n</body>\n</html></textarea>');
    d.write('<iframe id="iframe" style="flex:1;height:100%;"></iframe>');
    d.close();
    var s = d.body.style;
    s.display = 'flex';
    s.margin = 0;
    var i = d.getElementById('input');
    i.onkeydown = function(e) {
        if ((e.keyCode || e.which) != 9) {
            return;
        }
        e.preventDefault();
        var s = this.selectionStart;
        this.value = this.value.substring(0, s) + "  " + this.value.substring(this.selectionEnd);
        this.selectionEnd = s + 2;
    };
    i.select();
    var ifr = d.getElementById('iframe');
    i.addEventListener('click', function() {
        var idoc = ifr.contentWindow.document;
        idoc.open();
        idoc.write(i.value);
        idoc.close();
    });
    d.title = 'Textarea';
}(document));