WebSerial getPorts() method return nothing

I have tried Web Serial API.

If I use requestPort() method, like this :

<button id="connect">Connect</button>

<script>
    const connectButton = document.getElementById("connect");
    connectButton.addEventListener('click', async () => {
        try {
            const port = await navigator.serial.requestPort();
            console.log(port)
        } catch (e) {
            console.error(e)
        }
    });
</script>

It's OK, to prompt the user for which device the site should be allowed to control.

But with getPorts() method, like this :

<script>
    const connectButton = document.getElementById("connect");
    connectButton.addEventListener('click', async () => {
        try {
            const ports = await navigator.serial.getPorts();
            console.log(ports)
        } catch (e) {
            console.error(e)
        }
    });
</script>

I got nothing with ports.length == 0

Could anybody help this?

Thanks