If you are using jQuery and you want to add content to the existing contents of the div, you can use .html()
within the brackets:
$("#log").html($('#log').html() + " <br>New content!");
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<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>_x000D_
<div id="log">Initial Content</div>
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