What to work through
Work through a web app that works offline as a spoken system design interview. Start by clarifying the scope, sketch a working design and explain the trade-offs behind your choices.
- Open the app and read what was there with no connection
- Create and edit items offline, each change kept on the device at once
- Send changes made offline to the server when the connection returns, in the order they were made
- Settle changes when two devices edited the same item
- Show the person whether they are offline and which changes are not sent yet
Constraints to discuss
- A tap answers within 200 milliseconds, online or not
- No change made offline is lost or applied twice
- The app never blocks the screen while it waits for the network
- Kept data survives restarts, within what the browser lets the site keep
- The connection state is shown in words, not by colour alone
Need a starting point?
Watch for these common gaps as you prepare:
- Keeping waiting edits in memory, so closing the tab loses them
- Trusting the online flag to say the internet works
- Retrying a change with no id, so it is applied twice
- Assuming the browser keeps saved data forever
- Blocking the screen with a spinner while the network is down
Why this question is in the collection
These sources connect the problem to company interview reports or preparation guides. They do not guarantee what a company will ask you.