Example showing how to connect with a USB device using Javascript. Note that this file uses the chrome.usb.* API's which are only available for "packaged app" Chrome extensions.

gistfile1.js

var port = 0;
var endpoint = 0x01;
var device = { vendorId: 0x04b8, productId: 0x0202};

var connect = function(callback) {
  chrome.permissions.getAll(function(p) {
    if (p.permissions.indexOf('usb') >= 0) {

      //construct permission object for our device
      var obj = { usbDevices: [device] };

      //now request the permissions
      chrome.permissions.request({ permissions: [obj] }, function(granted) {
        if (granted) {
          chrome.usb.findDevices(device, function(devices) {
            if (devices && devices.length > 0) {
              //use the first found device
              var foundDevice = devices[0];
              //now lets reset the device
              chrome.usb.resetDevice(foundDevice, function() {
                //perform some error checking to make sure we reset the device
                if ( ! chrome.runtime.lastError) {
                  //now claim the interface using the port we specified
                  chrome.usb.claimInterface(foundDevice, port, function() {
                    if ( ! chrome.runtime.lastError) {
                      callback(foundDevice);
                    } else {
                      throw chrome.runtime.lastError.message;    
                    } 
                  })
                } else {
                  throw chrome.runtime.lastError.message;
                }
              });

            } else {
              console.warn("Device not found!");
            }
          });
        } else {
          console.warn("USB Permission not granted.")
        }
      });

    } else {
      console.warn("No USB permissions granted.");
    }
  });
}

@FrozenMaiden nop, didn't manage to, did you find a different solution?