Check one checkbox to select multiple checkboxes

I have a table where I'd like to be able to check one checkbox in the header to select all checkboxes in that table. This should normally be a quite straightforward thing, but it is simply not working here. When I run the sample code at JSfiddle it works. When running it in my development environment and checking the top box, if I put alert() it will alert, but still not check the rest of the checkboxes. Any ideas why?

[JS fiddle][1]

http://ift.tt/1xF1pzC