JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" value="test">
<input type="text" value="foobar">
<input type="password" value="">
<textarea>Lorem ipsum</textarea>
<br>
<div id="div"></div>

JavaScript

function getText(elem) {
    if(elem.tagName === "TEXTAREA" ||
       (elem.tagName === "INPUT" && elem.type === "text")) {
        return elem.value.substring(elem.selectionStart,
                                    elem.selectionEnd);
    }
    return null;
}

setInterval(function() {
    var txt = getText(document.activeElement);
    document.getElementById('div').innerHTML =
        txt === null ? 'no input selected' : txt;
}, 100);