Tag Archives: JavaScript

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) {
    showStatus(battery);
  });
} else if (!!navigator.battery) { // The old API is supported
  var battery = navigator.battery;
  showStatus(battery);
}

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

Status

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.

Status

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.

Status

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.

Twitter Bootstrap without jQuery

Twitter Bootstrap web pageThe more I use Twitter Bootstrap, the more I like it. The only thing that puts me off is needing jQuery for a few simple interactions such as hiding and displaying elements. jQuery’s an excellent library but if a site doesn’t make full use of it, it can be overkill, adding unnecessary bytes to your pages. As a replacement, I tried to make a lightweight alternative script specifically for Bootstrap.

Download it here

To use the script just put it in your pages, preferably at the bottom, instead of jQuery and the Bootstrap plugin scripts, like so:

    ...
    <script src="bootstrap-without-jquery.min.js"></script>
  </body>
</html>

The benefit is better performance thanks to faster page load times. It obviously doesn’t do everything that jQuery and the Bootstrap plugins do but it should be enough if you just want:

  • working dropdown menus;
  • dismissable alert boxes;
  • a collapsible navigation menu triggered by the “hamburger” button.

I tested it on several mobile and desktop browsers, including IE 8, but I’d appreciate further reports of where it does or doesn’t work. There may also be other Bootstrap components that require JavaScript so I can add support for those if there’s demand (or you can send a pull request). The GitHub page is here along with more details of browser support: github.com/tagawa/bootstrap-without-jquery

I’ve also prepared a simple Bootstrap demo page for testing. As always, feedback is welcome!

Update:

There’s also a good resource encouraging developers to use plain JavaScript where jQuery may not be necessary, with JavaScript code snippets that correspond to jQuery methods: YouMightNotNeedjQuery.com

List of JavaScript charting libraries

Illustration of some chart styles.I’m looking to make some pretty JavaScript charts and was wondering which library to use. I’ve used Flotr in an Opera extension and played around with gRaphaël in the past, but I want to do a more thorough comparison. First step is to list all the charting libraries I can find, so here it is…

Open source

Minimal or no dependencies

Require general-purpose library (e.g. jQuery)

Not open source

A few links for reference

Some are a little out-of-date but they’re still useful.