What's new in html5

New features of html5: 1. Semantic tags (header, footer, nav, etc.); 2. WebStorage storage mechanism; 3. History objects; 4. Form types (email, tell, date, etc.); 5. Media elements video and audio; 6. canvas.

The operating environment of this tutorial: Windows 7 system, HTML5 version, Dell G3 computer.

HTML5 is the next generation of HTML and will become the new standard for HTML, XHTML and HTML DOM.

HTML5 is the result of a collaboration between W3C and WHATWG.

Some rules established for HTML5:

• New features should be based on HTML, CSS, DOM and JavaScript.
• Reduce the need for external plug-ins (such as Flash)
• Better error handling
• More tags that replace scripts
• HTML5 should be device independent
• The development process should be transparent to the public

Browser support

The latest versions of Chrome, Firefox, Safari and Opera support certain HTML5 features. Internet Explorer 9 will support certain HTML5 features. The domestic Maxthon browser, as well as domestic browsers such as 360 Browser, Sogou Browser, QQ Browser, and Cheetah Browser based on IE or Chromium (the engineering version or experimental version of Chrome) also support HTML5 Ability.

New features

Some interesting new features added in HTML5:

1. Semantic tags

header<span style="font-family:Microsoft Yahei, Hiragino Sans GB, Helvetica, Helvetica Neue, 微软雅黑, Tahoma, Arial, sans-serif"> </span>footer , nav , aside , section , meau , template , article , audio , video , canvas etc.

2. webStorage Storage mechanism sessionStorage and localStorage

##webStorage: Use HTML5 to store user browsing data locally. Earlier, local storage was using cookies. But Web storage needs to be more secure and fast. These data will not be saved on the server, but these data will only be used when users request website data. It can also store large amounts of data without affecting website performance. Data exists in key/value pairs, and the data of a web page is only allowed to be accessed and used by that web page.

Web Storage is divided into two types: sessionStorage and localStorage, that is, these two are an instance of Storage. It can be clearly seen from the literal meaning that sessionStorage saves the data in the session and disappears when the browser is closed; while localStorage always saves the data locally on the client. The methods provided by its API are as follows:

setItem (key, value) ——  保存数据，以键值对的方式储存信息。

getItem (key) ——  获取数据，将键值传入，即可获取到对应的value值。

removeItem (key) ——  删除单个数据，根据键值移除对应的信息。

clear () ——  删除所有的数据

key (index) —— 获取某个索引的key

localStorage: data storage without time limit

The life cycle of localStorage is permanent. If you use localStorage to store data, even if you close the browser, the data will not disappear unless you actively delete the data. The method used is as shown above. localStorage has a length attribute, you can check how many records of data it has. The usage method is as follows:

var storage = null;                          //判断浏览器是否支持localStorage
    if(window.localStorage){
        storage.setItem("name", "Rick");     //调用setItem方法，存储数据
            alert(storage.getItem("name"));  //调用getItem方法，弹框显示 name 为 Rick
            storage.removeItem("name");      //调用removeItem方法，移除数据
            alert(storage.getItem("name"));  //调用getItem方法，弹框显示 name 为 null
    }

sessionStorage: Data storage for a session

The life cycle of sessionStorage is before the browser is closed. In other words, the data will always exist until the entire browser is closed. sessionStorage also has a length attribute, and its basic judgment and usage are the same as those of localStorage. The following points need to be noted:

(1) Refreshing the page will not erase the data;
(2) Only links opened on the current page can access sessionStorage data;
(3) Use window .open opens the page and changes the localtion.href method to obtain the data inside the sessionStorage;

3. History object

The history object saves the user's online history. , starting from the moment the window is opened.

Use the go() method to jump arbitrarily in the user's history, either backward or forward.

This method accepts a parameter, an integer value representing the number of pages to jump backward or forward.

Negative numbers represent jumping backward (similar to the "back" button of a stand-alone browser)

Positive numbers represent jumping forward (similar to the "forward" button of a stand-alone browser)

history.go(-1) // 后退一页 
history.go(1) // 前进一页 
history.go(2) // 前进两页

You can also pass a string parameter to the go() method. At this time, the browser will jump to the first position in the history that contains the string-----maybe forward or backward. . Depends on which location is closest. If the history does not contain the string, then this method does nothing

history.go('wrox.com') // 调到最近的 wrox.com 页面

You can also use the two shorthand methods back() and forward() instead of go(). Both methods mimic the browser's "back" and "forward" buttons.

history.back() // 后退一页
history.forward() // 前进一页

4. Upgrade of form elements

传统的表单元素：form、laber、textarea、select、button...

input（text、password、radio、checkbox、file、submit、reset、button）

Html5给input新增加一些类型（search、email、number、tell、range、color、date）

升级：给表单元素新增加属性placeholder（给表单元素设置提示信息）

升级：提供了新的下拉框方式

5、多媒体

用于回放的 video 和 audio 元素

6、用于绘画的 canvas

定义图形,绘制路径，矩形，圆形，字符以及添加图像的方法 。

　　首先创建canvas元素，并规定元素的id、宽度和高度撒的：

　　　　　　
　然后通过javas来绘制。Canvas元素本身没有绘图能力，所有的绘制工作必须在javascript内部完成渐变。
　　　　　　

　　JavaScript 使用 id 来寻找 canvas 元素：

　　　　　　var c=document.getElementById("myCanvas");

　　然后，创建 context 对象：

　　　　　　var cxt=c.getContext("2d");

　　getContext("2d") 对象是内建的 HTML5 对象，拥有多种绘制路径、矩形、圆形、字符以及添加图像的方法。

　　下面的两行代码绘制一个红色的矩形：

　　　　　　cxt.fillStyle="#FF0000";
　　　　　　cxt.fillRect(0,0,150,75);

　　fillStyle 方法将其染成红色，fillRect 方法规定了形状、位置和尺寸。

　　下面的两行代码绘制一条直线：

　　　　　　cxt.moveTo(100,100);

　　　　　　cxt.lineTo(200,200);

　　下面的一行代码是画一个圆：

　　　　　　cxt.arc(70,18,15,0,Math.PI*2,false);

　　这些属性值分别对应的是什么，70,18分别是X轴和Y轴，15是这个圆的半径，0是角度,Math.PI*2是圆周率，false代表顺时针而true是逆时针。

　　颜色的渐变效果也是可以实现的：

　　　　<script type="text/javascript">
　　　　　　　　var c=document.getElementById("myCanvas");
　　　　　　　　var cxt=c.getContext("2d");
　　　　　　　　var grd=cxt.createLinearGradient(0,0,175,50);
　　　　　　　　grd.addColorStop(0,"#FF0000");
　　　　　　　　grd.addColorStop(1,"#00FF00");
　　　　　　　　cxt.fillStyle=grd;
　　　　　　　　cxt.fillRect(0,0,175,50);
　　　　 </script>

　　还有一些其他效果:

　　　　曲线quadraticCurreTo

　　　　字体fillText

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