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Thursday, January 3, 2013

Very useful HTML5 APIs


The classList API provides the basic CSS controls our JavaScript libraries have been giving us for years:
// Add a class to an element

// Remove a class to an element

// Check for existence

// Toggle a class
The epitome of a great API addition: simple and intelligent.

ContextMenu API

The new ContextMenu API is excellent:  instead of overriding the browser context menu, the new ContextMenu API allows you to simply add items to the browser's context menu:
contextmenu="mymenu"> type="context" id="mymenu"> label="Refresh Post" onclick="window.location.reload();" icon="/images/refresh-icon.png"> label="Share on..." icon="/images/share_icon.gif"> label="Twitter" icon="/images/twitter_icon.gif" onclick="goTo('//' + document.title + ': ' + window.location.href);"> label="Facebook" icon="/images/facebook_icon16x16.gif" onclick="goTo('//' + window.location.href);">
Note that it's best to create your menu markup with JavaScript since JS is required to make item actions work, and you wouldn't want the HTML in the page if JS is turned off.


The dataset API allows developers to get and set data- attribute values:
/*  Assuming element:

// Get the element var element = document.getElementById("myDiv"); // Get the id var id =; // Retrieves "data-my-custom-key" var customKey = element.dataset.myCustomKey; // Sets the value to something else element.dataset.myCustomKey = "Some other value"; // Element becomes: //
Not much more to say; just like classList, simple and effective.

window.postMessage API

The postMessage API, which has even been supported in IE8 for years, allows for message sending between windows and IFRAME elements:
// From window or frame on domain 1, send a message to the iframe which hosts another domain
var iframeWindow = document.getElementById("iframe").contentWindow;
iframeWindow.postMessage("Hello from the first window!");

// From inside the iframe on different host, receive message
window.addEventListener("message", function(event) {
  // Make sure we trust the sending domain
  if(event.origin == "") {
    // Log out the message

    // Send a message back
    event.source.postMessage("Hello back!");
Messages may only be strings, but you could always use JSON.stringify and JSON.parse for more meaningful data!

autofocus Attribute

The autofocus attribute ensures that a given BUTTON, INPUT, or TEXTAREA element is focused on when the page is ready:
 autofocus="autofocus" />

Admittedly the autofocus attribute is disorienting for the visually impaired, but on simple search pages, it's the perfect addition.

Fullscreen API

The awesome Fullscreen API allows developers to programmatically launch the browser into fullscreen mode, pending user approval:
// Find the right method, call on correct element
function launchFullScreen(element) {
  if(element.requestFullScreen) {
  } else if(element.mozRequestFullScreen) {
  } else if(element.webkitRequestFullScreen) {

// Launch fullscreen for browsers that support it!
launchFullScreen(document.documentElement); // the whole page
launchFullScreen(document.getElementById("videoElement")); // any individual element
Any element can be pushed to fullscreen, and there's even a CSS pseudo-class to allow some control over the screen while in fullscreen mode.  This API is especially useful for JavaScript game development;

Page Visibility API

The Page Visibility API provides developers an event to listen in on, telling developers when the user focuses on a page's tab, and also when the user moves to another tab or window:
// Adapted slightly from Sam Dutton
// Set name of hidden property and visibility change event
// since some browsers only offer vendor-prefixed support
var hidden, state, visibilityChange; 
if (typeof document.hidden !== "undefined") {
  hidden = "hidden";
  visibilityChange = "visibilitychange";
  state = "visibilityState";
} else if (typeof document.mozHidden !== "undefined") {
  hidden = "mozHidden";
  visibilityChange = "mozvisibilitychange";
  state = "mozVisibilityState";
} else if (typeof document.msHidden !== "undefined") {
  hidden = "msHidden";
  visibilityChange = "msvisibilitychange";
  state = "msVisibilityState";
} else if (typeof document.webkitHidden !== "undefined") {
  hidden = "webkitHidden";
  visibilityChange = "webkitvisibilitychange";
  state = "webkitVisibilityState";

// Add a listener that constantly changes the title
document.addEventListener(visibilityChange, function(e) {
  // Start or stop processing depending on state

}, false);
When used properly, a developer can avoid expensive tasks (like AJAX polling or animating) when the tab isn't in focus.

getUserMedia API

The getUserMedia API is incredibly interesting;  this API provides access to device media, like your MacBook's camera!  Using this API, the
// Put event listeners into place
window.addEventListener("DOMContentLoaded", function() {
  // Grab elements, create settings, etc.
  var canvas = document.getElementById("canvas"),
    context = canvas.getContext("2d"),
    video = document.getElementById("video"),
    videoObj = { "video": true },
    errBack = function(error) {
      console.log("Video capture error: ", error.code); 

  // Put video listeners into place
  if(navigator.getUserMedia) { // Standard
    navigator.getUserMedia(videoObj, function(stream) {
      video.src = stream;;
    }, errBack);
  } else if(navigator.webkitGetUserMedia) { // WebKit-prefixed
    navigator.webkitGetUserMedia(videoObj, function(stream){
      video.src = window.webkitURL.createObjectURL(stream);;
    }, errBack);
}, false);
Look forward to using this API quite a bit in the future -- interactivity within the browser will be the norm a year from now!

Battery API

The Battery API is obviously a mobile-targeted API providing insight into the device's battery level and status:
// 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);
Knowing battery API and status can signal to the web application not to use battery-intensive processes and the like.  Not a groundbreaking API but surely a helpful one.

Link Prefetching

Link prefetching allows developers to silently preload site contents to project a more fluid, seamless web experience:

 rel="prefetch" href="" />

 rel="prefetch" href="" />

Browser support for each API differs, so use feature detection before using each API.  Take a few moments to read the detailed posts on each feature above -- you'll learn a lot and hopefully get a chance to tinker with each API!

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