Actually zip.js does use the Blob contructor when BlobBuilder is not available. Blob#slice is already used too. Anyway, I guess zip.js should look first for the presence of Blob constructor and then BlobBuilder constructor. The problem is that I don't know how to write Blob constructor feature test without a try/catch which I'd prefer not to use.

Okay. I just saw warnings in the console being thrown concerning it and no bug already open. As far as doing the test for it could you simply check what window.Blob returns? If it returns a function then you are good to use it if it returns something else switch to using the BlobBuilder.

I also noticed these warnings. I hope they will disappear soon ;). The test you suggested does not work on Safari 6. See this issue for more info: #15

I was really hoping that test would work. C'est la vie, alors!

Yes, the Blob type on Safari 6 has a certain je ne sais quoi that I find very annoying.