JavaScript Battery API

Mozilla Aurora 11 was recently released with a bevy of new features. One of those great new features is their initial implementation of the Battery Status API. This simple API provides you information about the battery's current charge level, its charging status, and allows you to be notified of changes via a few events. Let's check it out!

The battery object is located at window.navigator.battery, but since this is Mozilla's initial offering and the API is not yet cemented, you'll need to use window.navigator.mozBattery. The helpful mozBattery properties include:

• charging: Represents if the system's battery is charging. The attribute must be set to false if the battery is discharging, and set to true, if the battery is charging, full, the implementation is unable to report the state, or there is no battery attached to the system, or otherwise.
• chargingTime: Represents the time remaining in seconds until the system's battery is fully charged.
• dischargingTime: Represents the time remaining in seconds until the system's battery is completely discharged and the system is about to be suspended.
• level: Represents the current battery level scaled from 0 to 1.0. The attribute must be set to 0 if the system's battery is depleted and the system is about to be suspended, and to 1.0 if the battery is full, the implementation is unable to report the battery's level, or there is no battery attached to the system.

Events for each of these statuses are provided, including onchargingchange, onchargingtimechange, ondischargingtimechange, and onlevelchange. Basic usage is simple:

// Get the battery!
var battery = navigator.battery || navigator.webkitBattery || navigator.mozBattery;

// A few useful battery properties
console.warn("Battery charging: ", battery.charging); // true
console.warn("Battery level: ", battery.level); // 0.58
console.warn("Battery discharging time: ", battery.dischargingTime);

// Add a few event listeners
battery.addEventListener("chargingchange", function(e) {
	console.warn("Battery charge change: ", battery.charging);
}, false);
battery.addEventListener("chargingtimechange", function(e) {
	console.warn("Battery charge time change: ", battery.chargingTime);
}, false);
battery.addEventListener("dischargingtimechange", function(e) {
	console.warn("Battery discharging time change: ", battery.dischargingTime);
}, false);
battery.addEventListener("levelchange", function(e) {
	console.warn("Battery level change: ", battery.level);
}, false);

I promised a simple API, didn't I? The battery API is the perfect API: simple, effective, and focused!

So why use the battery API? Since many mobile apps live inside a browser wrapper (aren't completely "native"), it's great to have access to system information. Some processes are power-intensive and it may bear warning the user before starting the process that their device is low on battery. Either way, this simple API's true usefulness should become apparent soon!