I want to access socket.io.js trough an external js file (in my case called script.js), but I am getting the following error when trying to access trough the client side js file.

Uncaught ReferenceError: io is not defined

But when using js inside of my html it works fine. My Node.js API serves socket.io.js correctly and is accessable. Following html code works without errors.

<script src="/socket.io/socket.io.js"></script>
    <script>
        const socket = io();
        socket.on('message', function (message) {
        console.log(message);
        });

    </script>
</script>

While external js code doesn't work

const socket = io();
socket.on('message', function (message) {
console.log(message);
});

All js file are linked in head of my html