Clear web page history and block the back button!_javascript tips
This article introduces various solutions for disabling the browser back button that can be found on the Internet, and analyzes their respective advantages, disadvantages and applicable occasions.
1. Overview
Many people have asked, "How can I 'disable' the browser's back button?", or "How can I prevent users from clicking the back button to return to previously visited pages?" "This question is also one of the most frequently asked questions on the ASP forum. Unfortunately, the answer is very simple: we can't disable the browser's back
button.
At first I was incredulous that someone would want to disable the browser’s back button. Later, I was relieved to see that so many people wanted to disable the back button
(the only ones they wanted to disable were the back button, not the browser's forward button). Because by default, after submitting the form, the user can return to the form page through the
back button (instead of using the "Edit" button!), and then edit and submit the form again to insert new records into the database. This is something we
don’t want to see.
So I decided to find a way to avoid this situation. I visited many websites and consulted various implementation methods introduced by these websites. If you
frequently visit ASP programming websites, you may have seen some of the content introduced in this article. The task of this article is to introduce all possible methods to everyone, and then find
the best method!
2. Disable caching
Among the many solutions I found, one of them suggested disabling page caching. Specifically, use a server-side script as follows:
Response.ExpiresAbsolute = Now() - 1
Response.Expires = 0
Response.CacheControl = "no-cache"
%>
This method is very effective! It forces the browser to revisit the server to download the page instead of reading the page from cache. When using this method, the programmer's main task is to create a session-level variable that determines whether the user can still view the page that is not suitable for access via the back button. Since the browser
the user should be allowed to open the page.
For example, suppose we have the following form:
Response.Expires = 0
Response.CacheControl = "no-cache"
If Len(Session( "FirstTimeToPage")) > 0 then
&single; The user has visited the current page and is now returning to visit again.
&single; Clear session variables and redirect the user to the login page.
Session("FirstTimeToPage") = ""
Response.Redirect "/Bar.asp"
Response.End
End If
&single; If the program runs here, it means that the user can view Current page
&single; The following starts creating the form
%>
code:
Session("FirstTimeToPage") = "NO"
In this way, if the user who has opened SomePage.asp clicks the back button, the browser The server will be re-requested to download the page. The server checks that Session
("FirstTimeToPage") contains a value, so it clears Session("FirstTimeToPage") and redirects the user to other pages. Of course,
all of this requires the user to have cookies enabled, otherwise the session variables will be invalid. (For more explanation of this problem, see For session variables
to work, must the Web visitor have cookies enabled?)
In addition, we can also use client-side code to prevent the browser from caching Web pages:
If you use the above method to force the browser to no longer cache web pages, you must pay attention to the following points:
"Pragma: no-cache" only prevents the browser from caching the page when using a secure connection. For pages that are not protected by security, "Pragma: no-cache"
is treated the same as "Expires: -1". At this time, the browser still caches the page, but marks the page as expiring immediately.
In IE 4 or 5, the "Cache-Control" META HTTP-EQUIV tag is ignored and has no effect.
In practical applications we can add all these codes. However, since this method does not work in all browsers, it is not recommended. But
If it is an intranet environment and the administrator can control which browser the user uses, I think some people will still use this method.
3. Other methods
The method we are going to discuss next is centered on the back button itself, rather than the browser cache. Here is an article Rewiring the Back Button that is
worth referencing. However, I noticed that if this method is used, although the user will not see the page where he previously entered data when he clicks the back button, he only needs to click
twice. This is not the effect we want, because Many times, stubborn users are able to find ways to bypass preventive measures.
Another way to disable the back button is to use client-side JavaScript to open a window without a toolbar. This makes it difficult for the user to return to the previous page, but
not impossible. A safer, but rather annoying, method is to open a new window when the form is submitted and at the same time close the window where the form is located. But I feel
that this method is not worthy of serious consideration, because we can’t let users open a new window every time they submit a form.
So, can we add JavaScript code to the page that we don’t want users to return to? The JavaScript code added to this page can
be used to produce the effect of clicking the forward button, thus counteracting the action caused by the user clicking the back button. The JavaScript code used to implement this function is as follows
:
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