JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
<script src="https://code.jquery.com/jquery-2.1.4.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
<div class="container">
<form>
    <div class="row">
        <div class="col-md-6">
            Find:
            <textarea id="replaceID" rows="2" cols="10">to replace</textarea>
        </div>

        <div class="col-md-6">
            Replace with:
            <textarea id="withID" rows="2" cols="10">replaced with</textarea>
        </div>
    </div> 
    <div id="output_container" class="row">
        <div class="col-lg-6">
            <button type="button" onclick="go(replace);">Replace</button>
        </div>
        <div class="col-lg-6">
            Output:
            <textarea id="outID" rows="2" cols="10"></textarea>
        </div>
    </div>
</form>
</div>

JavaScript

function go(callback) {
    alert('go');
    callback('test');
};

function replace(output) {
    alert('rep');
};