Introduction to the role of hidden fields in html and usage examples

This article mainly introduces the role and usage examples of hidden fields in HTML. It has certain reference value. Now I share it with you. Friends in need can refer to it.

Hidden fields are on the page It is invisible to the user. The purpose of inserting a hidden field in the form is to collect or send information so that it can be used by the program that processes the form. The following is a detailed introduction to how this hidden field is used in practice. Friends who are interested should not miss it. Basic syntax:

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

Function:

1 Hidden fields are not visible to users in the page It can be seen that the purpose of inserting hidden fields in the form is to collect or send information so that it can be used by the program that processes the form. When the viewer clicks the send button to send the form, the hidden field information is also sent to the server.

2 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.

3 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.

4 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. .

5 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.

6 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 add 1 to the number when clicking the submit button

Number increases automatically.htm

Copy Code

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="_p" value="@n" /> 
<!-- <input name="txt" type="text" value="@value" />--> 
<p>@n</p> 
<input type="submit" value="click" /> 
</form>

Use the general handler to realize the

numerical increment.ashx

Copy code

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["_p"]; 
if (int.TryParse(s, out n)) 
{ 
n++; 
html = html.Replace("@n",n.ToString()); 
} 
} 
else 
{ 
//页面首次加载,给p和p对应的隐藏域赋值 
html = html.Replace("@n", n.ToString()); 
} 
context.Response.Write(html); 
}

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