Typescript join

<!DOCTYPE html>
<html lang="en-US">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Today's Date</title>
    <script>
        let competitionToday = "no competition"
        alert("Today there is " + competitionToday + "on");
    </script>
</head>
<body>
</body>
</html>

I can’t figure out why the

alert("Today there is " + competitionToday + "on");

is only alerting:
“Today there is no competition”
not:
“Today there is no competition on”