Beacons

Beacons is small library to send beacons to your server. It's basically a really minimal way of doing one way communication in browsers without any dependency on XHR requests or what ever. Internally it will use Image to do the actual requesting of the resource. So this method will not work when images are blocked. But it's still a great way to send additional debugging information to your server.

When you receive a beacon request on your server make sure you:

• Respond with a status code 204 and don't return any content.
• Don't add pointless HTTP headers to the response. Things such as Cookie headers are not needed and only add pointless bandwidth to these micro requests.

Once the beacon specification lands in the browsers we will start supporting it transparently. See http://w3c.github.io/beacon/ for the current working draft.

Installation

This module is only written for browser usage and assumes that a node.js module system is used for requiring the module. The module it self is released in npm and can be installed from the CLI using the following command:

npm install --save beacons

Usage

The API is as tiny as the module it self. It only exposes one function that does the request. This function accepts 3 arguments, the last 2 are optional.

1. url The URL you want to request.
2. fn An optional completion callback, it will be called when the resource is loaded, failed to load or times-out. It's not a guarantee that the message is actually send as that is nearly impossible to detect.
3. timeout The timeout before the callback is called. Defaults to 1000 ms.

So using this module is as simple as:

'use strict';

var beacon = require('beacons');

beacon('http://example.com/poke', function () {
  console.log('poked example.com');
});

Last but not least, the suggested code to handle the response on the server using Node.js

require('http').createServer(function (req, res) {
  res.statusCode = 404;
  if (req.url !== '/poke') return res.end('404');

  //
  // The actual code that handles the beacon, the code above is just routing of
  // the url..
  //
  res.statusCode = 204;                       // This prevents the need to send a body.
  res.setHeader('Cache-Control', 'no-cache'); // Browsers should never cache this.
  res.end(''); 
});

License

MIT