5 个强大的 HTML5 API

HTML5提供了一些非常强大的JavaScript和HTML API，来帮助开发者构建精彩的桌面和移动应用程序。本文将介绍5个新型的API，希望对你的开发工作有所帮助。 

1.  全屏API（Fullscreen API） 

该API允许开发者以编程方式将Web应用程序全屏运行，使Web应用程序更像本地应用程序。 

// 找到适合浏览器的全屏方法
function launchFullScreen(element) {
  if(element.requestFullScreen) {
    element.requestFullScreen();
  } else if(element.mozRequestFullScreen) {
    element.mozRequestFullScreen();
  } else if(element.webkitRequestFullScreen) {
    element.webkitRequestFullScreen();
  }
}

// 启动全屏模式
launchFullScreen(document.documentElement); // the whole page
launchFullScreen(document.getElementById("videoElement")); // any individual element

教程 / 演示 

2.  页面可见性API（Page Visibility API） 

该API可以用来检测页面对于用户的可见性，即返回用户当前浏览的页面或标签的状态变化。 

// 设置隐藏属性和可见改变事件的名称，属性需要加浏览器前缀
// 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";
}

// 添加一个标题改变的监听器
document.addEventListener(visibilityChange, function(e) {
  // 开始或停止状态处理
}, false);

教程 / 演示 

3.  getUserMedia API 

该API允许Web应用程序访问摄像头和麦克风，而无需使用插件。 

// 设置事件监听器
window.addEventListener("DOMContentLoaded", function() {
  // 获取元素
  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);
    };

  // 设置video监听器
  if(navigator.getUserMedia) { // Standard
    navigator.getUserMedia(videoObj, function(stream) {
      video.src = stream;
      video.play();
    }, errBack);
  } else if(navigator.webkitGetUserMedia) { // WebKit-prefixed
    navigator.webkitGetUserMedia(videoObj, function(stream){
      video.src = window.webkitURL.createObjectURL(stream);
      video.play();
    }, errBack);
  }
}, false);

教程 / 演示 

4.  电池API（Battery API） 

这是一个针对移动设备应用程序的API，主要用于检测设备电池信息。 

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

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

// 添加事件监听器
battery.addEventListener("chargingchange", function(e) {
  console.warn("Battery charge change: ", battery.charging);
}, false);

教程 

5.  Link Prefetching 

预加载网页内容，为浏览者提供一个平滑的浏览体验。 

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

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

教程