Index.js contains the source of babel-polyfill. The build minfies it with the reduce_vars option enabled. This causes a bug in chrome 51 (no other versions seem to be affected).
in the console:
expected output:
let str = 'fooBar'
str.split(/(?=[A-Z])/)
> ["foo", "Bar"]
actual output:
let str = 'fooBar'
str.split(/(?=[A-Z])/)
> ["fooBar"]