JSFiddle - React, Tailwind, and code Playground

HTML

<textarea>Some default text; HUlk is very cool innit</textarea>
<br/>

<input type="text" id="hulk" />

JavaScript

$('textarea').on('select', function() {
    var foo = getSelectionText();
    $('#hulk').val(foo);
});


function getSelectionText() {
    var text = "";
    if (window.getSelection) {
        text = window.getSelection().toString();
    } else if (document.selection && document.selection.type != "Control") {
        text = document.selection.createRange().text;
    }
    return text;
}