Building Spotify’s New Web Player

Thus, the team working on the Playlist view would implement a new feature, and make it available on the desktop application and the web player, without having to care about the underlying infrastructure. The web player, on the other hand, had to download many resources every time the user navigated between views, which resulted in long load times, which impacted user experience. There were a few key points behind the decision to rewrite the new web player from scratch versus improving the existing one:

We decided not to repeat the mistakes of the past, so before deciding the feature set that the new web player should have, we ran A/B tests on the existing web player.

Source: labs.spotify.com