The web application I'm working on aims to emulate traditional desktop applications and I'm finding it a challenge to implement Undo/Redo in this environment.

Undo/Redo has been in the specs since the beginning so it's not being tacked on late. It works when I run tests that do not use any of the commands that require interaction with the server. Most commands are handled in the browser and will take no perceptible amount of time to complete. Then there's the remote calls. In most cases the remote call will return in a flash but I have to account for those that don't.

Essentially, because the calls to the server will return asynchronously I am having issues with the commands finishing out of order.

My solution is to block the web application while these long running commands complete. I've tried to find an example of this in some desktop application but have so far come up empty.

Is blocking the application until a command finishes an acceptable solution to my problem?

EDIT A clarification The issue I am trying to solve has more to do with commands that take a long time to complete than server interaction. While a long processing command is running the user is free to continue making changes. These changes might be made on out of date data. I do not have an in browser command that takes a long time to complete so that is why I focused on the remote ajax calls. I apologize if this question is better suited to stackoverflow.

  • Check out (github.com/kriskowal/q). You might be able to chain ajax events to allow things to run in the order you need them to be. You can also chain events with JQuery ajax calls. – Andrew Jul 16 '14 at 16:16
  • If this is a limitation of the system, then it's not a matter of whether it's an acceptable solution. It's what you have to do. – nightning Jul 16 '14 at 16:28
  • Isn't this more of a StackOverflow kind of question? – Michael Lai Jul 16 '14 at 23:30

Option #1 - switch to Synchronous

Assuming you are using jQuery, you can set the following option:

    async: false

This will prevent the user from interacting with your app until the app receives and processes the response from the server.

Traditional desktop ctrl+z and such is syncronous but it's just so fast that you wouldn't know otherwise.

Option #2 - keeping it ASYNC

Another idea is to add these AJAX calls to a queue and process them one at a time in the background and display a "Syncing with server, DO NOT LEAVE THIS PAGE!" message somewhere notice-able. until it finishes.

  • Always use the latter. The first will give the browsrr the feeling that it crashed and even other tabs might not work anymore. Thats never a good expierence. – Hugo Delsing Jul 16 '14 at 17:03
  • I should clarify that the server would be returning new data that other commands can function on in the browser without making new remote calls. So I'd should queue all commands? Even if it means the app appears to lag behind? – Landstander Jul 16 '14 at 17:14
  • @Landstander I retract my previous statement, this should definitely be performed synchronously otherwise you will go bananas tracking bugs and issues. And you should probably put up a big and noticeable "Undoing, please wait" message – MonkeyZeus Jul 16 '14 at 17:45

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