Set your HTML as
<div id="body" hidden="">
<h1>Numbers</h1>
</div>
<div id="body1" hidden="hidden">
Body 1
</div>
And now set the javascript as
function changeDiv()
{
document.getElementById('body').hidden = "hidden"; // hide body div tag
document.getElementById('body1').hidden = ""; // show body1 div tag
document.getElementById('body1').innerHTML = "If you can see this, JavaScript function worked";
// display text if JavaScript worked
}