Covert string to code that can be performed (invoked, run, call and so on)

index.html

<!-- need bootstrap.css for quick start -->
<div class="container">
  <h2>Form control: textarea</h2>
  <p>The form below contains a textarea for comments:</p>
  <form role="form">
    <div class="form-group">
      <label for="comment">Comment:</label>
      <textarea class="form-control" rows="5" id="comment"></textarea>
      <button type="button" class="btn btn-default">Default</button>
    </div>
  </form>
</div>

script.js

var textarea = document.getElementsByTagName("textarea")[0];
textarea.value = "Hello World";
var button = document.getElementsByTagName("button")[0];
button.addEventListener("click", function () {
  (new Function(textarea.value))();
});