I just started learning Javascript, but I really thought I knew this. I can't figure out why it won't work. I need it to insert "this text" formatted as a level 2 header into theDiv when the button is clicked. I've tried every way, even with a function. This example seems like the way it should work, but doesn't. I have to make this work with Javascript only, no JQuery - I don't know any yet.
<html>
<h1 id="header">Header in progress</h1>
<body>
<p>
<input type="button" id="theButton" value="click me!" onclick="document.getElementById('theDiv').innerHTML('This is new.')">
</p>
<h3><div id="theDiv"></div></h3>
</body>
</html>