本地存储分为cookie，以及新增的localStorage和sessionStorage 。本篇章专门来讲讲 cookie
cookie
1、cookie 存储在本地，容量最大4k，在同源的http请求时携带传递，损耗带宽，可设置访问路径，只有此路径及此路径的子路径才能访问此cookie，在设置的过期时间之前有效。
jquery如果需要使用cookie，则需要一个插件js才可以使用。
已停止维护的Github地址：https://github.com/carhartl/jquery-cookie
访问下载jquery的cookie插件：http://plugins.jquery.com/cookie/
最新维护中的Github：https://github.com/js-cookie/js-cookie
本次采用最新维护中的Github采用的js。
Installation
Direct download
Download the script here and include it (unless you are packaging scripts somehow else):
<script src="/path/to/js.cookie.js"></script>
Or include it via jsDelivr CDN:
<script src="https://cdn.jsdelivr.net/npm/js-cookie@2/src/js.cookie.min.js"></script>
Do not include the script directly from GitHub (http://raw.github.com/...). The file is being served as text/plain and as such being blocked in Internet Explorer on Windows 7 for instance (because of the wrong MIME type). Bottom line: GitHub is not a CDN.
在Github里面举例了很多的用法，如下：
Basic Usage
Create a cookie, valid across the entire site:
Cookies.set('name', 'value');
Create a cookie that expires 7 days from now, valid across the entire site:
Cookies.set('name', 'value', { expires: 7 });
Create an expiring cookie, valid to the path of the current page:
Cookies.set('name', 'value', { expires: 7, path: '' });
Read cookie:
Cookies.get('name'); // => 'value'
Cookies.get('nothing'); // => undefined
Read all visible cookies:
Cookies.get(); // => { name: 'value' }
Note: It is not possible to read a particular cookie by passing one of the cookie attributes (which may or may not have been used when writing the cookie in question):
Cookies.get('foo', { domain: 'sub.example.com' }); // `domain` won't have any effect...!
The cookie with the name foo will only be available on .get() if it's visible from where the code is called; the domain and/or path attribute will not have an effect when reading.
Delete cookie:
Cookies.remove('name');
Delete a cookie valid to the path of the current page:
Cookies.set('name', 'value', { path: '' });
Cookies.remove('name'); // fail!
Cookies.remove('name', { path: '' }); // removed!
IMPORTANT! When deleting a cookie and you're not relying on the default attributes, you must pass the exact same path and domain attributes that were used to set the cookie:
Cookies.remove('name', { path: '', domain: '.yourdomain.com' });
Note: Removing a nonexistent cookie does not raise any exception nor return any value.
Namespace conflicts
If there is any danger of a conflict with the namespace Cookies, the noConflict method will allow you to define a new namespace and preserve the original one. This is especially useful when running the script on third party sites e.g. as part of a widget or SDK.
// Assign the js-cookie api to a different variable and restore the original "window.Cookies"
var Cookies2 = Cookies.noConflict();
Cookies2.set('name', 'value');
Note: The .noConflict method is not necessary when using AMD or CommonJS, thus it is not exposed in those environments.
JSON
js-cookie provides unobtrusive JSON storage for cookies.
When creating a cookie you can pass an Array or Object Literal instead of a string in the value. If you do so, js-cookie will store the string representation of the object according to JSON.stringify:
Cookies.set('name', { foo: 'bar' });
When reading a cookie with the default Cookies.get api, you receive the string representation stored in the cookie:
Cookies.get('name'); // => '{"foo":"bar"}'
Cookies.get(); // => { name: '{"foo":"bar"}' }
When reading a cookie with the Cookies.getJSON api, you receive the parsed representation of the string stored in the cookie according to JSON.parse:
Cookies.getJSON('name'); // => { foo: 'bar' }
Cookies.getJSON(); // => { name: { foo: 'bar' } }
Note: To support IE6-7 (and IE 8 compatibility mode) you need to include the JSON-js polyfill: https://github.com/douglascrockford/JSON-js
看完上面的基础用法之后，这里来写上一个基础完整的cookie操作设置和读取的用例：
注意：需要运行在服务器环境，就是例如使用nginx服务。直接html在浏览器访问是不会生成cookie的。
<!DOCTYPE html>
<html>
<head>
<title></title>
<meta charset="utf-8">
<script type="text/javascript" src="jquery/jquery-3.3.1.min.js"></script>
<script type="text/javascript" src="jquery/js.cookie.js"></script>
<script type="text/javascript">
$(function(){
// alert('hello');
// 设置cookie 过期时间为7天，存放在当前路径下
Cookies.set('name', 'value', { expires: 7, path: '' });
Cookies.set('cookie1', 'test_value1', { expires: 7, path: '' });
Cookies.set('cookie2', 'test_value2', { expires: 7, path: '' });
})
</script>
</head>
<body>
<h1>测试Cookies</h1>
</body>
</html>
访问浏览器如下：
下面再来读取cookie，如下：
<!DOCTYPE html>
<html>
<head>
<title></title>
<meta charset="utf-8">
<script type="text/javascript" src="jquery/jquery-3.3.1.min.js"></script>
<script type="text/javascript" src="jquery/js.cookie.js"></script>
<script type="text/javascript">
$(function(){
// Read cookie:
console.log( Cookies.get('name') ); // => 'value'
console.log( Cookies.get('cookie1') ); // => test_value1
console.log( Cookies.get('cookie2') ); // => test_value2
console.log( Cookies.get('nothing') ); // => undefined
})
</script>
</head>
<body>
<h1>测试Cookies</h1>
</body>
</html>
浏览器访问如下：
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