How do I load an HTML page in a div tag using JavaScript?

You can use the jQuery load function:

<div id="topBar">
    <a href ="#" id="load_home"> HOME </a>
</div>
<div id ="content">        
</div>

<script>
$(document).ready( function() {
    $("#load_home").on("click", function() {
        $("#content").load("content.html");
    });
});
</script>