1) I saw an interview question on this, and I'm assuming it's something to do with form submission and avoiding double submissions. Can someone confirm this?
2) Assuming this assumption is correct, can this be done with Ajax? If so is there a link someone can point me to?
(I'm assuming you'd generate some sort of random number and include it in the form as a hidden field, then ensure that number hadn't been submitted before for the session).
Redirect-after-post is a technique to avoid problems with the user refreshing or using the back button to get back to a posted form. In short, instead of providing a response page to an HTTP post, which will trigger another post if its reloaded, you issue a 303 redirect (or a 302, to support ancient browsers by taking advantage of a bug that is as old as the web). This causes the browser to issue a second HTTP request - a get this time - and if the response page to that is reloaded there shouldn't be any problems. Just make sure that all the changes are made by the post handler and the page you redirect to has no side effects.
If you post using XMLHttpRequest then the redirect will be followed; unless you specifically support it using the hash part of the location or the new HTML5 history methods then the back button and reload aren't going to trigger an AJAX post again.
Related
I am trying solve the back button issue within my app. The scenario is:
I have a home page with a search form which sends and receives data with $.ajax(), then the results loaded through ajax, their links points to a controller that won't be done by GET in ajax so that means that the page will be refreshed (so the home page with the results looks like this: http://url/en/home and a result link may look like this http://url/fetch/data/x123av).
The problem is which is the best way fix that when click back button to return the results from the search box?
I have found some answers in stackoverflow related to my question:
http://code.google.com/p/reallysimplehistory
http://tkyk.github.com/jquery-history-plugin
But from the documentation of those plugins, they all work by checking the hash change which I don't have.
Hope I have explained well enough, and I do have searched stackoverflow and google for a solution but I didn't find one that is close to this or either I've jumped over it...
Please just point me to the right way :D
But from the documentation of those plugins, they all work by checking
the hash change which I don't have.
If you want to handle the back button with AJAX request you will have to redesign your application so that it works with hashes as that's the only way. Changing the fragment portion of an url doesn't trigger a page reload but it is added to the history, so when you press the back button you are able to detect this change without navigating away from the page.
As mentioned by SLaks in the comments section another possibility is to use the HTML5 history API but obviously this assumes that the client browser supports it.
If you go to http://jsbin.com/ibozun/2, hit "Add Item," and then hit "Save," you will see that a second dialog is opened on top of the first one. The form in the dialog is posting to itself (no action defined) - this is by design. Because the dialog has duplicated itself, now you have to hit "Cancel" 2 times to get it to close.
The use-case for this setup is a MS MVC3 page with unobtrusive JQuery validation on it. The default scripts (in other words, I have no custom validators - the scripts are straight from MS) cause an ajax call to the server, and JQM treats that the same as a self-posting form - so you wind up with a duplicate dialog if validation fails.
A similar thing happens if the second page as a page, rather than a dialog - the form posting to itself results in a second history entry in the browser, so to get back to page 1, you have to hit back 2 times.
I believed this be a bug in JQM, but after submitting a bug on GitHub, I was told that this is the expected behavior. So, assuming this behavior that will not be changing in the framework, how do I prevent this from happening for my instance (preferring NOT to edit the framework JS)? Do I have to write my own ajax calls for validation so that I can prevent JQM from knowing that anything has happened? That seems unfortunate...
One idea I had was to detect that the nextPage and current page are the same on "pageHide", and manipulate the dialog/history myself, but have had no luck.
Thanks in advance!
First, there is no dialog duplication in the example. Second, my response and an explanation as to why solving the history issues with posting back to the same page for users of the library is hard can be found here. This example is particularly thorny because it's also in a dialog which we don't support linking to, so disabling ajax for the form (ie forcing it to reload), which would work if it were embedded in a page, won't serve.
The quick solution here is to switch the dialog to a page and add the data-ajax=false data attribute to the form. Mind you this causes a page flash/reload and requires that the form document be fully formed with a head including javascript,css, etc.
Is there any way I can change the URL or add more history to the "back button" without having to refresh the entire page?
My application is AJAX based and I'd like to add some "undo" events to history so that the user can simply hit back and retain the old values.
What's possible today? I hear some of this may be in HTML5 but haven't checked whats supported in current browsers.
I think you can use window.location.hash to track the #part of the page, in your case, #state1, #state2 and so on.
window.location.hash = '#state' + (++ stateN) to set and
stateN = parseInt(window.location.hash.match(/\d+$/)[0])
See On - window.location.hash - Change? for more details about how to detect location hash changes.
You could use 301 redirection. Personally, I would use cookies on the client side, or sessions in your back end, to store the breadcrumbs. Storing state information in the URL is a bad idea for AJAX applications, because people might return to a url that the server side is not in the right state to respond to.
Another option would be to provide your own Back button that knows which page to go back to.
The answer for this question will be more or less the same as my answers for these questions:
How to show Ajax requests in URL?
How does Gmail handle back/forward in rich JavaScript?
In summary, two projects that you'll probably want to look at which explain the whole hashchange process and using it with ajax are:
jQuery History (using hashes to manage your pages state and bind to changes to update your page).
jQuery Ajaxy (ajax extension for jQuery History, to allow for complete ajax websites while being completely unobtrusive and gracefully degradable).
It is possible to use ASP.NET's built in Script Manager to update the browser's history. A full how-to to do this is located here:
http://www.asp.net/aspnet-in-net-35-sp1/videos/introduction-to-aspnet-ajax-history
I read some paragraphs in a book saying that it is not possible to do a partial postback for web, even AJAX is employed. Ajax will postback everything and update only ajaxfied controls.
However, on pages I made using ajax, I used Fiddler to monitor the transportation. I found when the page initial load, it loaded everything include pictures .... However, when I click a button and do a ajax postback. I can only see the some data were loaded.... Looks like it doesn't need to reload the whole page again.
I don't know if what I see is correct? Or the book I read is correct?
Thank you guys.
That depends what you put in the term "postback".
The AJAX call will send the complete form data back to the server, just as if the form was posted normally. The server will answer with a partial response that only contains the parts of the page that should be updated.
So, the request is not partial, but the response is.
I am not sure how you are posting back from the client side. I am guessing you are using UpdatePanels. How well you 'AJAX-ify' a web page depends on what method you employ.
UpdatePanels - Read Dave Ward's posting on them - http://encosia.com/2007/07/11/why-aspnet-ajax-updatepanels-are-dangerous/
PageMethods to post back to a web service, get the data and update the DOM to display the result
JQuery and other such AJAX frameworks to post back to a web service
I am sure the link above should clear things up a bit
I'm having a hard time understanding your terminology. I'm not really sure what a "postback" is, much less a "partial" one. I do know that one of the basic ways to transmit information to an HTTP server is via a POST request, which is usually used when submitting forms. If you mean to say that the entire form is transmitted when you click a submit button, I believe you'd be right.
You also seem to be doing something with AJAX, but it's difficult to tell. The whole point of AJAX is to have dynamic data displayed on a page without resorting to reloading it. Defining what to send and what to do with the results is entirely up to your own JavaScript. So unless you're using a framework, which you don't specify, there is no such thing as "ajaxified controls."
In any case, "AJAX" usually means using the XMLHttpRequest() method of modern browsers to send data to servers without refreshing the page. When you call this function, you specify exactly what data to send. This has nothing to do with HTML forms. One caveat: if you are indeed using a library for AJAX, it might impose additional limits on how you structure information to send.
Greetings,
Here's the problem I'm having. I have a page which redirects directly to another page the first time it is visited. If the user clicks 'back', though, the page behaves differently and instead displays content (tracking session IDs to make sure this is the second time the page has been loaded). To do this, I tell the user's browser to disable caching for the relevant page.
This works well in IE7, but Firefox 3 won't let me click 'back' to a page that resulted in a redirect. I assume it does this to prevent the typical back-->redirect again loop that frustrates so many users. Any ideas for how I may override this behavior?
Alexey
EDIT: The page which we redirect to is an external site over which we have no control. Server-side redirects won't work because this wouldn't generate a 'back' button for in the browser.
To quote:
Some people in the thread are talking about server-side redirect, and redirect headers (same thing)... keep in mind that we need client-side redirection which can be done in two ways:
a) A META header - Not recommended, and has some problems
b) Javascript, which can be done in at least three ways ("location", "location.href" and "location.replace()")
The server side redirect won't and shouldn't activate the back button, and can't display the typical "You'll be redirected now" page... so it's no good (it's what we're doing at the moment, actually.. where you're immediately redirected to the "lucky" page).
I think the Mozilla team takes a step into the right direction by breaking this particularly annoying pattern. Finding a way around it somehow defies the purpose, doesn't it?
Instead of redirecting on first encounter, you could simply make your page render differently when a user hits it the first time. Should be easy enough on the server side, since you already have the code that is able to make that distinction.
You can get around this by creating an iframe and saving the state of the page in a form field in the iframe before doing the redirect. All browsers save the form fields of an iframe.
This page has a really good description of how to get it working. This is the same technique google maps uses when you click on map search results.
I'm strongly in favor for the Firefox behaviour.
The most basic way to redirect is to let the server send HTTP status code 302 + Location header back to the client. This way the client (typically a browser) will not place the request URI into its history, but just resend the same request to the advocated URI.
Now it seems that Firefox started to apply the bevaviour also for server responses that try redirections e.g. by Javascript's onload event.
If you want the browser not to display a page, I think the best solution is if the server does not send the page in the first place.
Its possibly in aide to eliminate repeated actions.
A lot of ways people do things is
page 1 -> [Action] -> page 2 -> redirect to page 2 without the action parameters.
Now if you were permitted to click the back button in this situation and visit the page without the redirect, the action would be blindly re-performed.
Instead, firefox presumes the server sent a redirect header for a good reason.
Although it is noted, that you can however have content delivered after the redirect header, sending a redirect header ( at least in php ) doesn't terminate execution, so in theory, if you were to ingnore the redirect request you would get the page doing weird stuff.
( I circumvent this by the fact all our redirects are done via the same function call, where i call an explicit terminate directly after the redirect, because people when coding assume this is how it behaves )
In the URL window of firefox type about:config
Change this setting in firefox
browser.sessionstore.postdata
Change from a 0 to 1