What is this the meaning of "Reload safe" web pages and can it be achieved with Ajax?

1开发者_如何学运维) 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).

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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.