Recently at an interview, I was asked to design Codesandbox. Interview went terrible. Here's the gist of what happened
I started from product requirements. To name a few -
[Functional]
<ol>
<li>User should be able to run programs JS - ecma support</li>
<li>User should be able to create folder structure</li>
<li>User should be able to download and install npm packages in the env.</li>
<li>Saving and sharing of programs</li>
<li>User should be able to preview (provide simulated browser env) programs</li>
<li>User should be able to deploy to different cloud envs [AWS, Heroku etc]</li>
</ol>
[Non functional] - Interviewer helped me with the topics as I wasnt able to think about it.
<ol>
<li>Auth</li>
<li>Different devices support -
a. Desktop + tablet - <a href="http://www">www</a>.
b. Mobile - PWA</li>
<li>Security -
a. Protection against bad programs</li>
<li>Performance -
a. Saving the state of the prog. At optimum intervals
b. Changes like creation of file/folder should be instant</li>
</ol>
Then we discussed mainly around different component interactions.
While designing component interactions, my mind always got stuck at the thought that how does the code gets evaluated and is shown in preview. All my responses were based on client-server interaction as I had seen for other languages like C, C++, or Java (This has come from my experience on coding on ideone.com during my college days). It was a wrong and immature thought and I was stuck at this.
Next it was detailing of UI components. Could come up with the following -
<ol>
<li>Editor
a. Notepad
b. FolderHierarchyView
i. FileControls
ii. CreateFile
iii. RenameFile</li>
<li>Preview
a. RefreshPreview
b. PreviewOutput
c. PreviewControls
d. PreviewConsole</li>
<li>Controls
a. Save
b. Share</li>
<li>App</li>
</ol>
Next up, we started discussing how program state will get saved. I was of the opinion that we shall not send whole program every time we want to save its state. It has to be done incrementally but I couldnt think of exact algorithm on how it could it be done.
Can someone please shed some light on this? How can we deal with questions like this? If someone has any blog refs, I would be very thankful.
I think it was SUPER HARD question for an hour interview.