JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="event_content">this text blah blah blah www.london2012.com that text blah blah blah www.london2012.com</textarea>

CSS

textarea {
    width:350px;
    height:100px;
}

JavaScript

$(function(){
    var old = $('#event_content').val();
    var news = old.replace("www.london2012.com", '<a href="http://www.rio2016.com" target="_blank">www.rio2016.com</a>');   
    $('#event_content').val(news);
});