Java Script Arrays Elements

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Arrays</h2>

<script>
let courses = ["HTML", "CSS", "JS"];
document.write( "<b> "+ courses +"</b> <br>");
courses[courses.length] = "PHP";
document.write( "<b> "+ courses +"</b>");

</script>

</body>
</html>