What is html hidden field

htmlHidden fields refer to form elements in web pages that are invisible to users, with the syntax "3e784ebd19ff8dc5ef5f2d4feb505168". The purpose of inserting hidden fields into a form is to collect or send information that can be used by the program that processes the form.

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

Hidden field: refers to the form elements in the web page that are invisible to users, that is, the form elements that are hidden.

Basic syntax:

<input type="hidden" name="field＿name" value="value">

Function:

Hidden fields are invisible to users on the page. The purpose of inserting hidden fields in the form is to collect or send information. To facilitate use by programs that process forms. When the viewer clicks the send button to send the form, the hidden field information is also sent to the server.

Sometimes we need to give the user information to determine the user's identity when submitting the form, such as session key, etc. Of course, these things can also be implemented using cookies, but it is much simpler to use hidden fields. And there will be no worries about browsers not supporting it and users disabling cookies.

Sometimes there are multiple submit buttons in a form. How can the program distinguish which button the user pressed to submit? We can write a hidden field, and then add onclick="document.form.command.value="xx"" to each button. Then after we receive the data, we first check the value of the command and we will know which one the user clicked. button to submit.

Sometimes there are multiple forms in a web page. We know that multiple forms cannot be submitted at the same time, but sometimes these forms do interact with each other. We can add hidden fields in the form to connect them.

Javascript does not support global variables, but sometimes we must use global variables. We can store the value in the hidden field first, and its value will not be lost.

There is another example. For example, four small windows pop up when you press a button. When one of the small windows is clicked, the other three automatically close. However, IE does not support small windows calling each other, so you can only write a hidden field in the parent window. When the small window sees that the value of the hidden field is close, it will close itself.

Example: Use hidden to increase the number by 1 when clicking the submit button

The value increases automatically.htm

The code is as follows:

<form action="数值自增.ashx" method="post"> 
<input type="hidden" name="_viewstate" value="a" /> 
<input type="hidden" name="_div" value="@n" /> 
<!-- <input name="txt" type="text" value="@value" />--> 
<div>@n</div> 
<input type="submit" value="click" /> 
</form>

Use a general handler to realize automatic numerical increment.ashx

The code is as follows:

int n = 0; 
public void ProcessRequest (HttpContext context) { 
context.Response.ContentType = "text/html"; 
string path = context.Request.MapPath("数值自增.htm"); 
string html = System.IO.File.ReadAllText(path); 
//判断页面是否是第一次加载 
string viewstate = context.Request.Form["_viewstate"]; 
if (!string.IsNullOrEmpty(viewstate)) 
{ 
//点击按钮 post 
//获取隐藏域的值 
string s = context.Request.Form["_div"]; 
if (int.TryParse(s, out n)) 
{ 
n++; 
html = html.Replace("@n",n.ToString()); 
} 
} 
else 
{ 
//页面首次加载,给div和div对应的隐藏域赋值 
html = html.Replace("@n", n.ToString()); 
} 
context.Response.Write(html); 
}

Recommended tutorial: "html video tutorial"

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