It appears to be checking whether the browser is Internet Explorer, and creating a Web Worker polyfill if it is - which, naming conventions aside, really isn't such a good strategy.

There's also a lot of `var foo` in that file; I don't know if it says much about the quality of code in the rest of the project (maybe this is just a file slapped together in a hurry), but it doesn't particularly inspire confidence.

In fact, on closer investigation, there's a lot of `var foo` in this file too: https://github.com/sloisel/numeric/blob/master/src/numeric.j...

The IE11 user agent looks like this:

  Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko