Tag Archives: devices

Responsive is not just visual: Three useful web APIs

A mobile user using a laptop outside.Mobile users are on the go. They’re rushing to get a train or busy meeting people. They don’t have much time and they’re on a slow connection. Right?

The answer of course is not necessarily. So-called mobile browsing could include shopping online while tucked up in bed, sending messages while watching TV or giggling at silly photos while relaxing in a cafe. It could also include being out and about but not using a mobile device.

In reality we have no idea what the users of our website are doing or where they are, and it would be a huge invasion of privacy if we did! Our fancy responsive designs should therefore not only look good but also be flexible enough to handle a variety of situations.

In other words, responsive doesn’t mean responding to screen size or even device capabilities. It means responding to the user’s environment (as much as possible).

But enough chatter. How can we do this in practice?

There are three handy web technologies that take us part of the way there: the Battery Status API, the Network Information API and Ambient Light Events. Support for all of them is mostly Chrome and Firefox for now, but keep an eye on caniuse.com and mobilehtml5.org for the latest support info. And now, on to the APIs…

Battery Status API

Why use it

Knowing whether your user is plugged in or not and whether their battery has much juice left can influence how your site reacts. Battery-draining features such as repeated actions and animations can be reduced or disabled, for example. Or you could notify the user and offer to save the current state in case there’s a sudden shutdown.

How to use it

The spec had a rewrite recently and now uses shiny new promises. The advantage of this is that the API is asynchronous, meaning that when you call the getBattery() method the browser makes sure the BatteryManager object is ready before you try to read its attributes. Those attributes are:

  • charging (a boolean)
  • chargingTime (in minutes)
  • dischargingTime (in minutes)
  • level (a number between 0 and 1)

Each of these attributes has an event so you can listen for when they change. In practice, you could use the attributes and events like this:

// Prepare a function to display the battery status
function showStatus(battery) {
  battery.onchargingchange = function () {
    console.log('Charging: ' + battery.charging);
  battery.onchargingtimechange = function () {
    console.log('Charging time remaining (mins): ' + battery.chargingTime);
  battery.ondischargingtimechange = function () {
    console.log('Discharging time remaining (mins): ' + battery.dischargingTime);
  battery.onlevelchange = function () {
    console.log('Battery level: ' + battery.level);

// Check for browser support first
if (!!navigator.getBattery) { // The latest API is supported
  // Use the battery promise to asynchronously call showStatus()
  navigator.getBattery().then(function(battery) {
} else if (!!navigator.battery) { // The old API is supported
  var battery = navigator.battery;

Guille Paz has made a nice battery status demo which includes code for the old and new versions of the spec.


This API has the best support of the three with Opera, Chrome and Firefox having implemented it. In the case of Firefox, the implementation currently uses an old version of the spec so for the time being it’s best to allow for both versions in your code.

Network Information API

Why use it

You’re probably aware of the navigator.onLine HTML5 attribute and its wide browser support but that only tells us if the user is connected to a network or not. For more detailed information about the network we need the aptly-named Network Information API. With the data it provides you could opt to show smaller or lower-quality images to users on slow connections, or only show a video background when you know the network speed is fast. Be careful when making assumptions though — wifi doesn’t necessarily mean fast.

How to use it

When fully implemented this provides the type and speed of connection using two attributes (type and downlinkMax) on the global navigator object. Let’s jump straight into an example…

// Some browsers use prefixes so let's cope with them first
var connection = navigator.connection || navigator.mozConnection || navigator.webkitConnection;

// Check for browser support
if (!!connection) {
  // Get the connection type
  var type = connection.type;

  // Get the connection speed in megabits per second (Mbps)
  var speed = connection.downlinkMax || connection.bandwidth;

So easy! The type values are a pre-defined selection of self-explanatory strings:

  • bluetooth
  • cellular
  • ethernet
  • none
  • wifi
  • wimax
  • other
  • unknown

Network speed, when available, is exposed as downlinkMax, previously called bandwidth, although in reality this is difficult for browsers to measure so it may be a while before we’re able to use it. You can also attach a change event listener to navigator.connection to be even more responsive.

For a more thorough look at this API and its background, Aurelio De Rosa has written a good tutorial and network information demo which I recommend.


In the browsers I tested only connection.type was supported properly and that was only in Chrome for Android and Firefox Mobile/OS (you may need to ensure dom.netinfo.enabled is set to true). It’s still early days for this API but its simplicity means it could easily be incorporated into your website or app.

Note: There is a version of the spec hosted on w3.org that currently says work on it has been discontinued. This refers to an older version and current work is being done in the GitHub-hosted version, which should eventually migrate to the W3C site.

Ambient Light Events

Why use it

We’re probably all familiar with struggling to read a screen in bright sunlight. Increasing the contrast of what’s displayed on the screen or hiding distracting backgrounds can make content much easier to read in such cases. The opposite is true — reducing how vivid a design is can avoid users screaming and covering their eyes when in a dark environment.

How to use it

Tomomi Imura, AKA @girliemac, has the definitive lowdown on how to respond to differing levels of light. Eventually we’ll all be able to use CSS4 media queries so when the light-level is dim, for example, we can respond accordingly. In the meantime though, there’s the more precise JavaScript approach which gives you access to data from the device’s light sensor. You just listen for a devicelight event and use that event’s value attribute to get the brightness of the user’s surroundings measured in lux. For example:

window.addEventListener('devicelight', function(e) {
  var lux = e.value;

  if (lux < 50) {
    // ambient light is dim so show lower-contrast version

See Tomomi's article for a more detailed example with added CSS and a link to her ambient light demo on CodePen.


At the time of writing support is only available in Firefox and Chrome beta for Android but here's a short video of her code in action:

Of course, these are not the only web technologies that are part of responsive web design but if you want to show the world that you know more than just media queries, they're a good place to start.

UPnP cheatsheet (and brief overview)

Printed out UPnP cheatsheetIn playing with UPnP and JavaScript (now possible thanks to the Network Service Discovery API), I’ve been trying to grasp how UPnP works and what’s possible with it. The potential of the technology is exciting but there seems to be a lack of basic, easy-to-digest information. So here you go — a simple cheatsheet for the main services of UPnP, concentrating on the audio/video subset (UPnP A/V).

Download: UPnP A/V Cheatsheet [PDF]

And whilst I’m at it, here’s the overall structure of UPnP in a nutshell:

  • UPnP contains ten categories for devices
  • Each device offers one or more services
  • Each service implements various functions
  • Each function requires zero or more parameters

For example, a PC could have a media server installed which would expose a ContentDirectory service, containing functions such as Browse and Search. Similarly, a TV could expose an AVTransport service (to play media) and a RenderingControl service (to control the device itself).