摘要：
数据存储是每一个站点必不可少的功能，在HTML5之前通过cookie可以实现本地数据存储。但是cookie只能存储4kb的数据，并且cookie是随http请求一起发送到服务端，这必然浪费了带宽。Web Storage是HTML5引入的一个非常重要的功能，可以在客户端本地存储数据，类似HTML4的cookie，但可实现功能要比cookie强大的多，Web Storage官方建议为每个网站5MB，每个浏览器存储数据大小不一致。
web storage分为两种，一种是localStorage，另一种是sessionStorage，两者的差别是sessionStorage会随着浏览器的关闭而被清楚掉，而localStorage会永久的保存在本地，除非人为的删除。数据是以对象的格式存储在本地，两种存储的方法是一样的。
浏览器:
方法：
增：
if(window.localStorage) {
localStorage.setItem('key', 'value');
}
删：
if(window.localStorage) {
localStorage.removeItem('key');
}
改：
与增方法一样
查：
if(window.localStorage) {
localStorage.getItem('key');
}
删除所有数据：
if(window.localStorage) {
localStorage.clear();
}
获取某个索引的key，或者是数据的key：
if(window.localStorage) {
localStorage.setItem('key', 'data');
console.log(localStorage.key('data')); // output key
}
扩展方法：
因为数据是以对象形式存在本地，索引对象的操作符也可以使用
if(window.localStorage) {
var storage = window.localStorage;
storage.key1 = "text";
storage["key2"] = "test";
console.log(storage.key1);
console.log(storage["key2"]);
}
key()与length实现数据遍历：
if(window.localStorage) {
var storage = window.localStorage;
for (var i=0, l = storage.length; i < l; i++) {
var key = storage.key(i);
var value = storage.getItem(key);
console.log(key + "=" + value);
}
}
window的storage事件：
当数据键值改变或者clear的时候，就会触发storage事件
if(window.localStorage) {
if(window.addEventListener) { // 非IE
window.addEventListener("storage",handler,false);
} else if(window.attachEvent) { // IE
window.attachEvent("onstorage",handler);
}
function handler(e){
}
}
事件对象属性：
| 属性 | 类型 | 描述 |
| key | String | 被添加、删除或者修改的key |
| oldValue | Any | 被修改、删除之前的值，如果是新增的则返回null |
| newValue | Any | 被修改、新增的值，如果是删除则返回null |
| url/uri | String | 当前页面地址 |
Demo：
下面这个实例是一个在线记事本，数据存储在localStorage中。分为两个页面，一个是填写数据，另一个是查看
edit.html
1 <!doctype html> 2 <html> 3 <head> 4 <title>LocalStorage</title> 5 <meta http-equiv="Content-Type" content="text/html;charset=utf-8"> 6 <style> 7 #count { 8 width: 500px; 9 height: 500px; 10 background-color:#D3D3D3; 11 margin:0 auto; 12 } 13 </style> 14 <script src="http://cdn.staticfile.org/jquery/2.0.0/jquery.min.js"></script> 15 </head> 16 <body> 17 <form method="post" action=""> 18 <textarea id="count" name="count"></textarea><br /> 19 <input type="button" name="button" id="sub" value="提交"> 20 </form> 21 <script> 22 $(function(){ 23 var data = new Array(); 24 var json =""; 25 var storage = window.localStorage; 26 27 $("#sub").click(function(){ 28 if(!storage.getItem("content")){ 29 storage.setItem("content", JSON.stringify($("#count").val().split('\n'))); 30 } else { 31 var content = JSON.parse(storage.getItem("content")); 32 if($.isArray(content)) { 33 storage.setItem("content", JSON.stringify(content.concat($("#count").val().split('\n')))); 34 } else { 35 storage.setItem("content", JSON.stringify($("#count").val().split('\n').push(content))); 36 } 37 } 38 $("#count").val(""); 39 location.href = 'see.html'; 40 }); 41 }) 42 </script> 43 </body> 44 </html>
see.html
1 <!doctype html> 2 <html> 3 <head> 4 <title>NoteBook</title> 5 <meta http-equiv="Content-Type" content="text/html;charset=utf-8"> 6 <style> 7 #conten { 8 background-color: #E1C97F; 9 width: 500px; 10 height: 600px; 11 margin: 0 0 0 500px; 12 } 13 .stor { 14 padding: 10px 10px; 15 border-bottom: 1px dotted black; 16 } 17 .check { 18 float: right; 19 } 20 #back { 21 margin-left: 700px; 22 } 23 </style> 24 <script src="http://cdn.staticfile.org/jquery/2.0.0/jquery.min.js"></script> 25 </head> 26 <body> 27 <div id="conten"> 28 </div> 29 <input type="button" name="button" id="back" value="返回"> 30 <script> 31 $(function(){ 32 var storage = window.localStorage; 33 var newjson = JSON.parse(storage.getItem('content')); 34 for(var i=0;i<newjson.length;i++){ 35 var htm = "<p class='stor'>"+newjson[i]+"</p>"; 36 $(htm).appendTo("#conten"); 37 } 38 $('#back').click(function() { 39 location.href = 'edit.html'; 40 }); 41 }); 42 </script> 43 </body> 44 </html>
效果图
附录：
| Topic | Description |
|---|---|
| HTMLStorage |
Represents the list of key/value pairs that have been assigned to a single storage area. |
| clear |
Removes all key/value pairs from the Web Storage area. |
| getItem |
Retrieves the current value associated with the Web Storage key. |
| initStorageEvent |
Initializes a new Document Object Model (DOM) storage event that thecreateEvent method created. |
| key |
Retrieves the key at the specified index in the collection. |
| removeItem |
Deletes a key/value pair from the Web Storage collection. |
| setItem |
Sets a key/value pair. |
| key |
Gets the key that is updated. |
| length |
Retrieves the length of the key/value list. |
| localStorage |
Retrieves the Web Storage area specific to the current document. |
| newValue |
Gets the new value of the key. |
| oldValue |
Gets the previous value of the key. |
| remainingSpace |
Retrieves the remaining memory space, in bytes, for the storage object. |
| sessionStorage |
Retrieves the Web Storage area for the session. |
| storageArea |
Gets the Storage object of the affected document. |
| url |
Gets the address of the document that the update affects. |
