[javascript] TypeError: document.getElementbyId is not a function

function showSource() {_x000D_
  var content = document.getElementbyId("edit").innerHTML_x000D_
  content.replace(/</g, '&lt;');_x000D_
  content.replace(/>/, '&gt: ');_x000D_
  prompt("Your Code:", content);_x000D_
_x000D_
}_x000D_
_x000D_
function createLink() {_x000D_
  var url = prompt("Enter URL:", "http://");_x000D_
  if (url)_x000D_
    document.execCommand("createlink", false, url);_x000D_
}

<h1>Native Rich Text</h1>_x000D_
<p>No textboxes here, that's a &lt;div&gt; element!</p>_x000D_
<div>_x000D_
  <input type="button" value="Bold" onclick="document.execCommand('bold', false, null);">_x000D_
  <input type="button" value="Italic" onclick="document.execCommand('italic', false, null);">_x000D_
  <input type="button" value="Underline" onclick="document.execCommand('underline', false, null);">_x000D_
  <input type="button" value="Add Link" onclick="createLink();">_x000D_
  <input type="button" value="Show Source" onclick="showSource();">_x000D_
</div>_x000D_
<div id="edit" style="border:solid black; height: 300px; width: 400px;" contenteditable="true">_x000D_
  Hello!_x000D_
</div>