Element definition HTML form
Form elements refer to different types of input elements, check boxes, radio buttons, submit buttons, etc.
HTML forms are used to collect different types of user input.
<form><span style="color: #000000;"> . form elements . </span></form>
elements have many forms, according to different type attributes.
This is the type used in this chapter: (there are also password, checkbox, button, etc.)
| Type | Description |
|---|---|
| text | Define regular text input. |
| radio | Define radio button inputs (select one of multiple choices) |
| submit | Define submit button (submit form) |
HTML5 adds several new input types:
Note: Input types not supported by old web browsers will be treated as input type text.
Here are some commonly used input restrictions (some of which are new in HTML5):
| Property | Description |
|---|---|
| disabled | Specifies that input fields should be disabled. |
| max | Specifies the maximum value of the input field. |
| maxlength | Specifies the maximum number of characters for the input field. |
| min | Specifies the minimum value of the input field. |
| pattern | Specifies the regular expression by which the input value is checked. |
| readonly | Specifies that input fields are read-only (cannot be modified). |
| required | Specifies that the input field is required (required). |
| size | Specifies the width of the input field in characters. |
| step | Specifies legal number intervals for input fields. |
| value | Specify the default value of the input field. |
定义单选按钮。
单选按钮允许用户在有限数量的选项中选择其中之一：
<form> <input type=<span style="color: #800000;">"</span><span style="color: #800000;">radio</span><span style="color: #800000;">"</span> name=<span style="color: #800000;">"</span><span style="color: #800000;">sex</span><span style="color: #800000;">"</span> value=<span style="color: #800000;">"</span><span style="color: #800000;">male</span><span style="color: #800000;">"</span> <span style="color: #0000ff;">checked</span>><span style="color: #000000;">Male </span><br> <input type=<span style="color: #800000;">"</span><span style="color: #800000;">radio</span><span style="color: #800000;">"</span> name=<span style="color: #800000;">"</span><span style="color: #800000;">sex</span><span style="color: #800000;">"</span> value=<span style="color: #800000;">"</span><span style="color: #800000;">female</span><span style="color: #800000;">"</span>><span style="color: #000000;">Female </span></form>
定义用于向表单处理程序（form-handler）提交表单的按钮。
表单处理程序通常是包含用来处理输入数据的脚本的服务器页面。
表单处理程序在表单的 action 属性中指定：
<form action=<span style="color: #800000;">"</span><span style="color: #800000;">action_page.php</span><span style="color: #800000;">"</span>><span style="color: #000000;"> First name:</span><br> <input type=<span style="color: #800000;">"</span><span style="color: #800000;">text</span><span style="color: #800000;">"</span> name=<span style="color: #800000;">"</span><span style="color: #800000;">firstname</span><span style="color: #800000;">"</span> value=<span style="color: #800000;">"</span><span style="color: #800000;">Mickey</span><span style="color: #800000;">"</span>> <br><span style="color: #000000;"> Last name:</span><br> <input type=<span style="color: #800000;">"</span><span style="color: #800000;">text</span><span style="color: #800000;">"</span> name=<span style="color: #800000;">"</span><span style="color: #800000;">lastname</span><span style="color: #800000;">"</span> value=<span style="color: #800000;">"</span><span style="color: #800000;">Mouse</span><span style="color: #800000;">"</span>> <br><br> <input type=<span style="color: #800000;">"</span><span style="color: #800000;">submit</span><span style="color: #800000;">"</span> value=<span style="color: #800000;">"</span><span style="color: #800000;">Submit</span><span style="color: #800000;">"</span>> </form>
action 属性定义在提交表单时执行的动作。
向服务器提交表单的通常做法是使用提交按钮。
通常，表单会被提交到 web 服务器上的网页。
在上面的例子中，指定了某个服务器脚本来处理被提交表单：
<form action=<span style="color: #800000;">"</span><span style="color: #800000;">action_page.php</span><span style="color: #800000;">"</span>>
如果省略 action 属性，则 action 会被设置为当前页面。
method 属性规定在提交表单时所用的 HTTP 方法（GET 或 POST）
<form action=<span style="color: #800000;">"</span><span style="color: #800000;">action_page.php</span><span style="color: #800000;">"</span> method=<span style="color: #800000;">"</span><span style="color: #800000;">GET</span><span style="color: #800000;">"</span>><span style="color: #000000;"> 或： </span><form action=<span style="color: #800000;">"</span><span style="color: #800000;">action_page.php</span><span style="color: #800000;">"</span> method=<span style="color: #800000;">"</span><span style="color: #800000;">POST</span><span style="color: #800000;">"</span>>
您能够使用 GET（默认方法）：
如果表单提交是被动的（比如搜索引擎查询），并且没有敏感信息。
当您使用 GET 时，表单数据在页面地址栏中是可见的：
action_page.php?firstname=Mickey&lastname=Mouse
注释：GET 最适合少量数据的提交。浏览器会设定容量限制。
您应该使用 POST：
如果表单正在更新数据，或者包含敏感信息（例如密码）。
POST 的安全性更加，因为在页面地址栏中被提交的数据是不可见的。
如果要正确地被提交，每个输入字段必须设置一个 name 属性。
本例只会提交 "Last name" 输入字段，因为“First name“没有设置 name 属性：
<form action=<span style="color: #800000;">"</span><span style="color: #800000;">action_page.php</span><span style="color: #800000;">"</span>> First name:
"text" value="Mickey">
Last name:
"text" name="lastname" value="Mouse">
"submit" value="Submit">
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