files/en-us/web/api/usbdevice/opened/index.md
{{APIRef("WebUSB API")}}{{SeeCompatTable}}{{SecureContext_Header}}{{AvailableInWorkers}}
The opened read only property of the
{{domxref("USBDevice")}} interface indicates whether a session has been started with a
paired USB device. A device must be opened before it can be controlled by a web page.
A {{jsxref("boolean")}}.
This example is for a hypothetical USB device with a multi-colored LED. It shows how to test that a device is open before calling {{domxref("USBDevice.controlTransferOut")}} to set a specified LED color.
[!NOTE] What data can be passed to a USB device and how it is passed is particular and unique to each device.
async function setDeviceColor(usbDevice, r, g, b) {
if (device.opened) {
// This hypothetical USB device requires that the data passed to
// it be in a Uint8Array.
const payload = new Uint8Array([r, g, b]);
await usbDevice.controlTransferOut(
{
requestType: "vendor",
recipient: "device",
request: 1,
value: 0,
index: 0,
},
payload,
);
}
}
{{Specifications}}
{{Compat}}