USBDevice.opened - Web APIs 编辑

Experimental

This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The opened read only property of the 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.

Syntax

var serialNumber = USBDevice.opened

Value

A boolean.

Example

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 USBDevice.controlTransferOut to set a specified LED color.

What data can be passed to a USB device and how it is passed is particular and unique to each device. 

async setDeviceColor(usbDevice, r, g, b) {
   if (device.opened) {
     // This hypothetical USB device requires that the data passed to
     // it be in a Uint8Array.
     let payload = new Uint8Array([r, g, b]);

     await usbDevice.controlTransferOut({
       requestType: 'vendor',
       recipient: 'device',
       request: 1,
       value: 0,
       index: 0,
     }, payload);
   }
 }

Specifications

Browser compatibility

BCD tables only load in the browser