html5 Web儲存的localStorage和sessionStorage的使用方法【圖文說明】
<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title></title> <style type="text/css"> textarea { width: 300px; height: 300px; } .button { width: 100px; }</style> </head> <body onload="init()"> <script type="text/javascript"> //使用HTML5 Web儲存的localStorage和sessionStorage方式進行Web頁面資料本地儲存。 //頁面參考如下圖,能將頁面上的資料進行本地儲存。並能讀取儲存的資料顯示在頁面上。 var t1; var t2; var oStorage; var oStorage; functioninit() {//初始化t1,t2 t1 = document.getElementById("t1"); t2 = document.getElementById("t2"); sStorage = window.sessionStorage; lStorage = window.localStorage } function saveSession() { sStorage.mydata = t2.value; t1.value+= "sessionStorage儲存mydata:" + t2.value + "\n"; } function readSession() { t1.value += "sessionStorage讀取mydata:" + sStorage.mydata + "\n"; } function cleanSession() { t1.value += "sessionStorage清除mydata:" + sStorage.mydata + "\n"; sStorage.removeItem("mydata"); } function saveStorage() { lStorage.mydata = t2.value; t1.value += "localStorage儲存mydata:" + t2.value + "\n"; } function readStorage() { t1.value += "localStorage讀取mydata:" + lStorage.mydata + "\n"; } function cleanStorage() { t1.value += "localStorage清除mydata:" + lStorage.mydata + "\n"; lStorage.removeItem("mydata"); } </script> <div> <textarea id="t1"></textarea><br /> <label>需要儲存的資料: </label> <input type="text" id="t2" /><br /> <input type="button" class="button" onclick="saveSession()" name="b1" value="session儲存" /> <input type="button" class="button" onclick="readSession()" value="session讀取" /> <input type="button" class="button" onclick="cleanSession()" value="session清除" /><br /> <input type="button" class="button" onclick="saveStorage()" value="local儲存" /> <input type="button" class="button" onclick="readStorage()" value="local讀取" /> <input type="button" class="button" onclick="cleanStorage()" value="local清除" /> </div> </body> </html>
首先自然是檢測瀏覽器是否支援本地儲存。在HTML5中,本地儲存是一個window的屬性,包括localStorage和sessionStorage,從名字應該可以很清楚的辨認二者的區別,前者是一直存在本地的,後者只是伴隨著session,視窗一旦關閉就沒了。二者用法完全相同,這裡以localStorage為例。
if(window.localStorage){
alert('This browser supports localStorage');
}else{
alert('This browser does NOT support localStorage');
}
儲存資料的方法就是直接給window.localStorage新增一個屬性,例如:window.localStorage.a 或者 window.localStorage["a"]。它的讀取、寫、刪除操作方法很簡單,是以鍵值對的方式存在的,如下:
localStorage.a = 3;//設定a為"3"
localStorage["a"] = "sfsf";//設定a為"sfsf",覆蓋上面的值
localStorage.setItem("b","isaac");//設定b為"isaac"
var a1 = localStorage["a"];//獲取a的值
var a2 = localStorage.a;//獲取a的值
var b = localStorage.getItem("b");//獲取b的值
localStorage.removeItem("c");//清除c的值
這裡最推薦使用的自然是getItem()和setItem(),清除鍵值對使用removeItem()。如果希望一次性清除所有的鍵值對,可以使用clear()。另外,HTML5還提供了一個key()方法,可以在不知道有哪些鍵值的時候使用,如下:
var storage = window.localStorage;
function showStorage(){
for(var i=0;i<storage.length;i++){
//key(i)獲得相應的鍵,再用getItem()方法獲得對應的值
document.write(storage.key(i)+ " : " + storage.getItem(storage.key(i)) + "<br>");
}
}
寫一個最簡單的,利用本地儲存的計數器:
var storage = window.localStorage;
if (!storage.getItem("pageLoadCount")) storage.setItem("pageLoadCount",0);
storage.pageLoadCount = parseInt(storage.getItem("pageLoadCount")) + 1;//必須格式轉換
document.getElementByIdx_x("count").innerHTML = storage.pageLoadCount;
showStorage();
不斷重新整理就能看到數字在一點點上漲,如下圖所示:
需要注意的是,HTML5本地儲存只能存字串,任何格式儲存的時候都會被自動轉為字串,所以讀取的時候,需要自己進行型別的轉換。這也就是上一段程式碼中parseInt必須要使用的原因。
另外,在iPhone/iPad上有時設定setItem()時會出現詭異的QUOTA_EXCEEDED_ERR錯誤,這時一般在setItem之前,先removeItem()就ok了。
HTML5的本地儲存,還提供了一個storage事件,可以對鍵值對的改變進行監聽,使用方法如下:
if(window.addEventListener){
window.addEventListener("storage",handle_storage,false);
}else if(window.attachEvent){
window.attachEvent("onstorage",handle_storage);
}
function handle_storage(e){
if(!e){e=window.event;}
//showStorage();
}
對於事件變數e,是一個StorageEvent物件,提供了一些實用的屬性,可以很好的觀察鍵值對的變化,如下表:
Property |
Type |
Description |
key |
String |
The named key that was added, removed, or moddified |
oldValue |
Any |
The previous value(now overwritten), or null if a new item was added |
newValue |
Any |
The new value, or null if an item was added |
url/uri |
String |
The page that called the method that triggered this change |
這裡新增兩個鍵值對a和b,並增加一個按鈕。給a設定固定的值,當點選按鈕時,修改b的值:
<body>
<p>You have viewed this page <span id="count">0</span> time(s).</p>
<p><input type="button" value="changeStorage" onClick="changeS()"/></p>
<script>
var storage = window.localStorage;
if (!storage.getItem("pageLoadCount")) storage.setItem("pageLoadCount",0);
storage.pageLoadCount = parseInt(storage.getItem("pageLoadCount")) + 1;//必須格式轉換
document.getElementByIdx_x("count").innerHTML = storage.pageLoadCount;
showStorage();
if(window.addEventListener){
window.addEventListener("storage",handle_storage,false);
}else if(window.attachEvent){
window.attachEvent("onstorage",handle_storage);
}
function handle_storage(e){
if(!e){e=window.event;}
showObject(e);
}
function showObject(obj){
//遞迴顯示object
if(!obj){return;}
for(var i in obj){
if(typeof(obj[i])!="object" || obj[i]==null){
document.write(i + " : " + obj[i] + "<br/>");
}else{
document.write(i + " : object" + "<br/>");
}
}
}
storage.setItem("a",5);
function changeS(){
//修改一個鍵值,測試storage事件
if(!storage.getItem("b")){storage.setItem("b",0);}
storage.setItem('b',parseInt(storage.getItem('b'))+1);
}
function showStorage(){
//迴圈顯示localStorage裡的鍵值對
for(var i=0;i<storage.length;i++){
//key(i)獲得相應的鍵,再用getItem()方法獲得對應的值
document.write(storage.key(i)+ " : " + storage.getItem(storage.key(i)) + "<br>");
}
}
</script>
</body>
測試發現,目前瀏覽器對這個支援不太好,僅iPad和Firefox支援,而且Firefox支援得亂糟糟,e物件根本沒有那些屬性。iPad支援非常好,用的是e.uri(不是e.url),桌上型電腦上的Safari不行,詭異。
localStorage實現本地快取 的一個完整的例子:HTML程式碼
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>本地快取</title>
<script type="text/javascript">
var Cookie = {};
Cookie.read = function (name) {
var cname = name + "=";
var dc = document.cookie;
if (dc.length > 0) {
begin = dc.indexOf(cname);
if (begin != -1) {
begin += cname.length;
end = dc.indexOf(";", begin);
if (end == -1) end = dc.length;
return dc.substring(begin, end); //www.camnpr.com
}
}
return null;
}
Cookie.write = function (name, value) {
var expire = "";
var hours = 365;
expire = new Date((new Date()).getTime() + hours * 3600000);
expire = ";path=/;expires=" + expire.toGMTString();
document.cookie = name + "=" + value + expire;
}
var strKey = "strKey";
var storage = window.localStorage;
function onStart(){
if(storage.getItem(strKey)!=null){
alert(storage.getItem(strKey)+'localStorage');
}else if(Cookie.read(strKey)!=null){
alert(Cookie.read(strKey)+'cookie');
}
}
function bendihuancun(){
var strValue = document.getElementById("username").value;
if (storage) {
storage.setItem(strKey, strValue);
} else {
Cookie.write(strKey, strValue);
}
} //www.camnpr.com
</script>
</head>
<body onload="onStart()">
<input type="text" id="username" value="camnpr">
<input type="button" value="儲存快取" onclick="bendihuancun()">
</body>
</html>