In my previous post, I proposed some enhancements to improve Shufflizer’s transaction integrity. These are done and in production now. They are:
- The count of songs is confirmed on download and upload
- A temporary backup copy of the playlist is uploaded when doing same-playlist upload, and then deleted only if the same-playlist upload succeeds
I just wound up doing more callbacks
Most of the enhancements needed procedural (aka. synchronous) processing. “Don’t do the following step, and don’t accept user input, until the current step finishes ok.” I looked for something in ReactiveX’s JavaScript implementation to do this (RXJS), but did not find one. Perhaps JavaScript’s await would have done it, but I realized that I could:
- make steps run in series using the usual approach – callbacks
- prevent user input with something I already had – the loading spinner
So I proceeded with additional layers of callbacks and moved my command that closes the loading spinner to the bottom layer.
What I mean by a callback is a procedure that is called after the Observable, which is asynchronous, returns a value. In this example deletePlaylist “calls back” to getPlaylists. getPlaylists does not run until deletePlaylist returns a value:
this.spotSvc.deletePlaylist(b_plId,accessToken).subscribe(()=>this.getPlaylists(userId, userCountry, accessToken));