JSFiddle - React, Tailwind, and code Playground

HTML

Описание:<br /> <textarea id='opis' type="text" cols="60" rows="6"/></textarea>
<br />
<span id='opis1'></span>

JavaScript

function fReplce(a) {
    var b = {
        "Петя": "Вася",
        "Катя": "Аня"
    };
    for (var c in b) {
        var d = RegExp(c, "gim");
        a = a.replace(d, b[c])
    }
    return a
};
$("#opis").keyup(function () {
     var value = $(this).val();
     $("#opis1").text( fReplce( value ) );
   }).keyup();