JSFiddle - React, Tailwind, and code Playground

HTML

select me selet me select me select me.  select me selet me select me select me.  select me selet me select me select me.  select me selet me select me select me.  select me selet me select me select me.  select me selet me select me select me.

JavaScript

if (!window.x) {
    x = {};
}

x.Selector = {};
x.Selector.getSelected = function() {
    var t = '';
    if (window.getSelection) {
        t = window.getSelection();
    } else if (document.getSelection) {
        t = document.getSelection();
    } else if (document.selection) {
        t = document.selection.createRange().text;
    }
    return t;
}

$(document).ready(function() {
    $(document).bind("mouseup", function() {
        var mytext = x.Selector.getSelected();
        alert(mytext);
    });
});