If minified web-animations-js is run with 'use strict' at the top of the file, there is an error: `Uncaught TypeError: Cannot set property 'true' of undefined` coming from https://github.com/web-animations/web-animations-js/blob/master/web-animations-next-lite.min.js#L15. This is due to the fact that a global "this" is undefined in strict mode, rather than the window. The iife is called like: function(a, b) { b["true"] = ...... } ({}, function {return this}())