Summary of HTML5 storage methods

This article mainly shares with you a summary of HTML5 storage methods. I hope it can help HTML5 developers and help everyone better master HTML5 storage methods.

1. The Savage Growth of Cookies

2. Local Storage localstorage

3. Local Storage sessionstorage

4. Offline cache (application cache)

5. Web SQL

6. IndexedDB

The barbaric growth of Cookies

Before HTML5 appeared, Cookies occupied the entire world of client storage, just like the barbaric growth of the barbaric era. cookiesMeet the needs of practical applications well and quickly. But its problems are also obvious. cookies will carry data in the request header, and the size is limited to 4K, which is very unsafe and easy to be intercepted by the outside. There are also domainpollute.

IE The browser especially likes to create its own set. To increase the storage capacity, UserData is added. The size is 64K, but other browsers The computer doesn't like to play with it, so it is the only one that supports it.

Then, here comes the point. Since there are so many problems with cookies, we must find ways to solve them, otherwise we will not be able to move forward. First identify its problems and then find solutions based on those problems.

• Solve 4KStorage capacity problem

• Solve the problem of request headers with storage information, which is to increase security , data storage and transmission through encrypted channels or methods

• Solving the problem of relational storage

• Cross-browser

Local storage localstorage

Storage method

Stored in the form of key-value pairs, permanently stored, and will never expire unless Delete manually.

Storage capacity

5M per domain name.

Commonly used API

getItem //Get the record

setItem //Set the record

removeItem //Remove the record

key //Get the value corresponding to key

clear //Clear the record

Local storage sessionstorage

Local storage of HTML5localstorage# in API ## and sessionstorage are the same in usage. The difference is that sessionstorage will be cleared after closing the page, while localstorage will always be saved unless manually delete. Offline cache (application cache)

Local cache files required by the application

Usage method

1. Configuration

manifest

FileOn page:

nbsp;HTML>

...

manifestFile:

manifest

Is the simplest text file that tells the browser what is cached (and what is not cached).

manifestThe file is divided into three parts:

1. CACHE MANIFEST

   - In this title The files listed below will be cached after the first download

2. NETWOrK

   - Files under this heading require a connection to the server and will not be cached

3. FALLBACK

   - The files under this heading specify the fallback page when the page cannot be accessed (such as the 404 page)

Complete

demo

CACHE MANIFEST
# 2016-07-24 v1.0.0
/theme.css
/main.js

NETWORK:
login.jsp

FALLBACK:
/html/ /offline.html

On the server:

manifest file needs to be configured correctly MIME-type, which is text/cache-manifest.

Commonly used

APIThe core is the

applicationCache

object, which has a status attribute, indicating the application The current status of the cache:

0 (UNCACHED)

: No cache, no application cache related to the page

1 (IDLE)

: Idle , the application cache has not been updated

2 (CHECKING)

: Checking, downloading the description file and checking for updates

3 (DOWNLOADING)

: Downloading, the application cache is downloading the resources specified in the description file

4 (UPDATEREADY)

: The update is completed, all resources have been downloaded

5 (IDLE)

: Abandoned, the application cache description file no longer exists, so the page can no longer access the application cache

Related events

indicates the application cache status Changes to:

checking

: Triggered when the browser is looking for updates for the app cache

error

: An error occurred during checking for updates or downloading a resource Triggered when

noupdate

: Triggered when checking the description file and found that the file has no changes

downloading

: Triggered when starting to download application cache resources

progress

: Triggered when the file download application cache continues to download

updateready

: Triggered when the new application cache download of the page is completed

cached

: Triggered when the application cache is fully available

Three advantages of application cache:

1. 离线浏览

2. 提升页面载入速度

3. 降低服务器压力

注意事项：

1. 浏览器对缓存数据的容量限制可能不太一样（某些浏览器设置的限制是每个站点5M）

2. 如果是manifest文件，或者内部列举的某一个文件不能正常下载，整个更新过程将视为失败，浏览器继续全部使用旧的缓存

3. 引用manifest的html必须与manifest文件同源，在同一个域下

4. 浏览器会自动缓存引用manifest文件的html文件，这就导致了如果更改了html内容，也需要更新版本才能做到最新

5. manifest文件中的CACHE与NETWOrK、FALLBACK的位置顺序没有关系，如果是隐式声明需要在最前面

6. FALLBACK中的资源必须和manifest文件同源

7. 更新完版本后，必须刷新一次才会启动新版本（会出现重刷一次页面的情况），需要添加监听版本事件

8. 站点中的其他页面即使没有设置manifest属性，请求的资源如果在缓存中也从缓存中访问

9. 当manifest文件发生改变时，资源请求本身也会触发更新

离线缓存和传统浏览器缓存的区别

1. 离线缓存是针对整个应用，浏览器缓存是单个文件

2. 离线缓存可以主动通知浏览器更新资源

Web SQL

Web SQL数据库API并不是HTML5规范的一部分，但它是一个独立的规范，引入了一组使用SQL操作客户端数据库的APIs。

核心方法

1. openDatabase：使用现有的数据库或新建的数据库创建一个数据库对象

2. transaction： 控制一个事务，以及基于这种情况执行提交或回滚

3. executeSql：用于执行实际的SQL查询

打开数据库

var db = openDatabase('mydb', '1.0', 'TEST DB', 2 * 1024 * 1024, fn);

执行查询操作

var db = openDatabase('mydb', '1.0', 'TEST DB', 2 * 1024 * 1024);
db.transaction(function (tx) {
    tx.executeSql('CREATE TABLE IF NOT EXISTS WIN (id unique, name)');
})

插入数据

注：博客主题里的代码块样式

var db = openDatabase('mydb', '1.0', 'Test DB', 2 * 1024 * 1024);
db.transaction(function (tx) {
   tx.executeSql('CREATE TABLE IF NOT EXISTS WIN (id unique, name)');
   tx.executeSql('INSERT INTO WIN (id, name) VALUES (1, "winty")');
   tx.executeSql('INSERT INTO WIN (id, name) VALUES (2, "LuckyWinty")');
});

注：需要实现的代码块样式，这个是 markdowpad2 里的操作，也是很多markdown写作工具提供的操作，只需要按一下 tab 键，非常方便

var db = openDatabase('mydb', '1.0', 'Test DB', 2 * 1024 * 1024);
db.transaction(function (tx) {
   tx.executeSql('CREATE TABLE IF NOT EXISTS WIN (id unique, name)');
   tx.executeSql('INSERT INTO WIN (id, name) VALUES (1, "winty")');
   tx.executeSql('INSERT INTO WIN (id, name) VALUES (2, "LuckyWinty")');
});

读取数据

db.transaction(function (tx) {
   tx.executeSql('SELECT * FROM WIN', [], function (tx, results) {
      var len = results.rows.length, i;
      msg = "<p>查询记录条数: " + len + "</p>";
      document.querySelector('#status').innerHTML +=  msg;

      for (i = 0; i <h2 id="IndexedDB">IndexedDB</h2><p>索引数据库（<code>IndexedDB</code>）<code>API</code>（作为<code>HTML5</code>的一部分）对创建具有丰富本地存储数据的数据密集型的离线<code>HTML5 Web</code>应用程序很有用，同时它还有助于本地缓存数据，使传统在线<code>Web</code>应用程序（比如移动<code>Web</code>应用程序）能够快速的运行和响应。</p><p><strong>异步<code>API</code></strong></p><p>在<code>IndexedDB</code>大部分操作并不是我们常用的调用方法（返回结果的模式），而是（请求-响应模式），比如打开数据库的操作。</p><p>相关推荐：</p><p><a href="http://www.php.cn/html5-tutorial-361331.html" target="_self">前端HTML5几种存储方式的总结</a></p><p><a href="http://www.php.cn/js-tutorial-340047.html" target="_self">JavaScript中变量的存储方式</a></p><p><a href="http://www.php.cn/php-weizijiaocheng-302975.html" target="_self">在PHP中自定义session的存储方式_PHP教程</a></p><p class="comments-box-content"><br></p>

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