Develop Reference

Web Bluetooth - Auto Connect to paired device

Is there a way to auto connect to a paired device with the web Bluetooth ?
So i can get rid of the annoying pop up device selector from google..

As of this moment, I have implemented navigator.bluetooth.getDevices() behind a flag in Chrome. To use the API, the Experimental Web Platform features flag in chrome://flags needs to be enabled. Please follow Issue 577953: bluetooth: Get permitted devices for updates on getDevices().
For reconnecting to a device, I'm also implementing the watchAdvertisements() API to allow apps to receive an Event when system perceives an advertisement packet from device on which this was called on. Please follow Issue 654897: bluetooth: Implement watchAdvertisements() for updates on this API.
These two are part of a bigger project for implementing persistent permissions for Web Bluetooth to allow sites to reconnect to devices that they already had permission to connect to via the device chooser prompt.

Chrome WebUSB not recognizing devices (CAC cards, smart cards)

I have made a script to load all of the USB devices connected to Chrome using chrome.usb.getDevices. So far, it has listed a second-generation iPod touch as well as a mouse, keyboard, and two unknown items from Intel. However, it has not recognized any USB flash drives, and it does not recognize any Smart Cards that I have. I've also installed Chrome's Smart Card Connector app into Chrome, but I can still not get Chrome to recognize these Smart Cards. I can't continue to use Java nor ActiveX to for smartcard interactions in the browser. How can I get CAC/smartcard authentication through the browser without having to install a slew of other dependencies?
Edit: I also installed WinUSB as their drivers in place of their default HID drivers, but the results remained.

This Chrome USB Devices states that not all USB devices are supported and can be read:
Caveats
Not all devices can be accessed through the USB API. In general,
devices are not accessible because either the Operating System's
kernel or a native driver holds them off from user space code. Some
examples are devices with HID profiles on OSX systems, and USB pen
drives.
On most Linux systems, USB devices are mapped with read-only
permissions by default. To open a device through this API, your user
will need to have write access to it too. A simple solution is to set
a udev rule. Create a file /etc/udev/rules.d/50-yourdevicename.rules
with the following content:
SUBSYSTEM=="usb", ATTR{idVendor}=="[yourdevicevendor]", MODE="0664", GROUP="plugdev"

Browser Chat Without internet

Can anyone explain me the possibilities of creating a web chat (i.e similar to whatsappweb) which works without internet connections the only possible way that these device communicate is either by WiFi or Bluetooth (i.e Peer to peer). If it is not possible on earth could then explain why?
I've come across some javascript files like peer.js. But it uses internet i think. I want it to work without internet connectivity.
Thanks in advance.

With WebRTC it is possible to establish peer-to-peer communication between web-browsers in the same local network: https://developer.mozilla.org/en-US/docs/Web/Guide/API/WebRTC/Peer-to-peer_communications_with_WebRTC
A server is only needed for communication outside of a local network: http://blog.vline.com/post/63765098884/webrtc-if-its-p2p-why-do-i-need-a-server
There is another demonstration in this page: https://hacks.mozilla.org/2013/05/embedding-webrtc-video-chat-right-into-your-website/
However WebRTC is a relatively new system that is not widely supported - so consider it experimental at this stage - but it has the backing of Mozilla, so it might end-up somewhere.
However you are limited to the capabilities that WebRTC provides - and as your code is still JavaScript that runs in the browser you will not have access to any kind of actual networking API (such as Berkeley Sockets) or lower-level control of hardware, such as the ability to create Ad-hoc Wi-Fi networks, new Bluetooth Personal Area Networks, or LE Bluetooth connections... at present.
Google is working on making a Bluetooth API available that runs in the browser. Presently it is only available to Chrome Extensions, but it may soon be available in web-pages in general: https://developers.google.com/web/updates/2015/07/interact-with-ble-devices-on-the-web

Ofcourse there is a way to make this happen. You would have to set up a webserver on the device with this webapp. You could then connect with localhost or 127.0.0.1 . Other people would have to join your hotspot and connect to your ip address.
If you want to connect automaticly you would have to write a real app.

Browsers run in a "contained" mode. No hardware access is possible from any script ran inside the browser, thus there's no way to initialize and setup the device to start direct communication.

How to initiate a new device pairing using the Chrome web bluetooth API?

Using navigator.bluetooth.requestDevice(), I can access bluetooth devices I've already set up a pair with using native OSX bluetooth pairing, but no previously-unpaired devices appear, even when their attributes match my generic query. Available devices show up in a Chrome modal requesting user consent to pair, but the only device that shows up is the one I've already paired with.
Am I misunderstanding the intended use case here, or is there another way to establish a connection with a nearby (previously unpaired) device from Chrome?
Docs: https://webbluetoothcg.github.io/web-bluetooth/
(See Example 2)
function bluetoothConnect() {
navigator.bluetooth.requestDevice({filters: [{services: ['generic_access']}]})
.then(device => {console.log(`Connected to: ${device.name}`)})
.catch(console.error);
}

First, Mac OS X is not yet fully implemented as we speak. Only discovery and GATT server connect/disconnect are working for now. See the Chrome Implementation status at https://github.com/WebBluetoothCG/web-bluetooth/blob/gh-pages/implementation-status.md. Check out Chrome OS, Linux and Android M (Android Lollipop workaround).
Regarding your specific issue, I believe that generic_access is not broadcasted by a nearby BLE device but is found because you've already paired (cached) this device. If your device is named "foo" for instance, you can go to https://googlechrome.github.io/samples/web-bluetooth/device-info.html and fill "foo" as the Device Name and hit "Get Bluetooth Device Info" button.
I would recommend you give a try to all Web Bluetooth samples at https://googlechrome.github.io/samples/web-bluetooth/index.html as well.

To complement the other answer, please be aware of the Chrome's chrome://bluetooth-internals tab/tool. This tool can not only list available devices and their services (which I don't think you can do with the Web Bluetooth API unless you requested the services in optionalServices or filters/services) and the characteristics of those services.
In the device list, there is a Forget button which becomes active once you connect to the devices GATT server using the Inspect button. This should allow you to full unpair and pair again in cases where you need to test the flow end to end.
Edit: Actually after doing some experimentation around this, the device still remains paired even after using the Forget button. Probably a bug in Chrome, however, the cache of the paired devices seems to be per-profile. This means the real answer is to:
Use the Incognito mode and in there the pairing flow will initiate from the get-go for each new Incognito session.

How do Stack Overflow desktop notifications work?

Perhaps this is a fairly big and ambiguous question:
In the Stack Overflow chatrooms, there is a button to "enable desktop notifications," which will show something in the system tray when someone replies to you.
By what mechanism does this work? It's always made me curious.
How does a website access the system tray?

It uses the Notification object (i.e. var n = new Notification("Hello");) to provide local notifications on a per-website basis. Each browser implements the standard differently (see Chrome, Firefox, and Safari), but they all operate essentially the same way, sending notifications based on the permissions they have (window.Notification.permission), which can be default (hasn't been asked, in which case you would window.Notification.requestPermission();), granted, or denied. Opera and Internet Explorer do not support desktop notifications at this time.

They're called Desktop Notifications, which use the Notifications API.
Basically, the site checks for Notifications API support, then the user grants or denies the website permission to display notifications.
Here is more information on how the API works.

This is with the help of WebSockets - Web APIs. There is actually a persistent connection between the client and the server. And also both parties can start sending data at any time.