What are the minimum JS requirements for the Playback SDK?

[nolani12]

I'm looking to implement the Playback SDK in a JavaFX app using the WebView component. The aim is for the JavaFX interface to control the player, and the player is just there as a skeleton to play music (since the only way to do playback currently is the JS SDK). The WebView uses WebKit and an older version of JavaScript - I believe at least ECMAScript 3.

When I try to load the player using the sample code, none of the listener functions are called. However, I do know the onSpotifyWebPlaybackSDKReady function is getting called.

Can I get the player to work properly in this case or do I need a more modern embedded browser?