5 個強大的 HTML5 API

HTML5提供了一些很是強大的JavaScript和HTML API，來幫助開發者構建精彩的桌面和移動應用程序。本文將介紹5個新型的API，但願對你的開發工做有所幫助。 

1.  全屏API（Fullscreen API） 

該API容許開發者以編程方式將Web應用程序全屏運行，使Web應用程序更像本地應用程序。 

// 找到適合瀏覽器的全屏方法
function launchFullScreen(element) {
  if(element.requestFullScreen) {
    element.requestFullScreen();
  } else if(element.mozRequestFullScreen) {
    element.mozRequestFullScreen();
  } else if(element.webkitRequestFullScreen) {
    element.webkitRequestFullScreen();
  }
}

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

教程 / 演示 

2.  頁面可見性API（Page Visibility API） 

該API能夠用來檢測頁面對於用戶的可見性，即返回用戶當前瀏覽的頁面或標籤的狀態變化。 

// 設置隱藏屬性和可見改變事件的名稱，屬性須要加瀏覽器前綴
// 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";
}

// 添加一個標題改變的監聽器
document.addEventListener(visibilityChange, function(e) {
  // 開始或中止狀態處理
}, false);

教程 / 演示 

3.  getUserMedia API 

該API容許Web應用程序訪問攝像頭和麥克風，而無需使用插件。 

// 設置事件監聽器
window.addEventListener("DOMContentLoaded", function() {
  // 獲取元素
  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);
    };

  // 設置video監聽器
  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.  電池API（Battery API） 

這是一個針對移動設備應用程序的API，主要用於檢測設備電池信息。 

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

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

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

教程 

5.  Link Prefetching 

預加載網頁內容，爲瀏覽者提供一個平滑的瀏覽體驗。 

<!-- 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