Nigina,
Вариант ...
<!DOCTYPE html>
<html>
<head>
<title></title>
<style>
.highligt
{
background:#FF3;
}
</style>
</head>
<body>
<script type="text/javascript">
var text = 'Chocolate Chocolate <a target="_blank" href="blabla dot ru/wiki/Chocolate " title="Chocolate">Chocolate</a> Chocolate Chocolate';
text = text.replace(/(Chocolate)(?=[^>]*?<|[^>]*?$)/gi, "<span class='highligt'>$1</span>" );
document.write(text);
</script>
</body>
</html>