JSFiddle - React, Tailwind, and code Playground

HTML

<textarea></textarea>

JavaScript

function text_diff(first, second) {
        var start = 0;
        while (start < first.length && first[start] == second[start]) {
            ++start;
        }
        var end = 0;
        while (first.length - end > start && first[first.length - end - 1] == second[second.length - end - 1]) {
            ++end;
        }
        end = second.length - end;
        return second.substr(start, end - start);
}
$('textarea').bind('paste', function() {
    var self = $(this);
    var orig = self.val();
    setTimeout(function() {
        var pasted = text_diff(orig, $(self).val());
        console.log(pasted);
    });
});