5个不可错过的HTML 5中的API
  这次接着介绍5个更多HTML 5的API。这些API还是很实用的。

1 fullscreen全屏api,可惜不是全部浏览器支持，播放视频，做游戏时有用
   

function launchFullScreen(element) {
  if(element.requestFullScreen) {
    element.requestFullScreen();
  } else if(element.mozRequestFullScreen) {
    element.mozRequestFullScreen();
  } else if(element.webkitRequestFullScreen) {
    element.webkitRequestFullScreen();
  }
}

// Launch fullscreen for browsers that support it!
launchFullScreen(document.documentElement);

launchFullScreen(document.getElementById("videoElement")); //点单独的与元素时启动 

2 page visiablity页面可见性判断的API
   这个可以用来判断当用户的焦点不在当前tab的时候触发，下面这个例子，当CHROME下运行时候，如果新建立一个TAB，并且焦点到了新的tab，则会发现原来的页面的标题的title属性显示为"hidden"了
  

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);

不错的关于这个功能的详细教程：
http://davidwalsh.name/page-visibility

3 getUserMedia api 获得访问媒体设备的API
   可以允许调用用户的媒体设备，比如camera等。

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); 
    };

  // 播放
  if(navigator.getUserMedia) { // Standard
    navigator.getUserMedia(videoObj, function(stream) {
      video.src = stream;
      video.play();
    }, errBack);
  } else if(navigator.webkitGetUserMedia) { // WebKit系列浏览器    navigator.webkitGetUserMedia(videoObj, function(stream){
      video.src = window.webkitURL.createObjectURL(stream);
      video.play();
    }, errBack);
  }
}, false);

 

  更具体的教程见：
http://davidwalsh.name/browser-camera


4 电池API
   可以获得电池的工作状态

var battery = navigator.battery || navigator.webkitBattery || navigator.mozBattery;


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

//电池的监听 
battery.addEventListener("chargingchange", function(e) {
  console.warn("Battery charge change: ", battery.charging);
}, false);

    这个对移动设备很有效果，相关教程：
http://davidwalsh.name/battery-api
可惜这东西暂时只自mozilla下有效果

5 页面元素预加载 prefetch
  主要是浏览器加载完页面后，将其放到浏览器的cache中去，

<link rel="prefetch" href="http://davidwalsh.name/css-enhancements-user-experience" />


<link rel="prefetch" href="http://davidwalsh.name/wp-content/themes/walshbook3/images/sprite.png" />

  教程：http://davidwalsh.name/html5-prefetch