IE9 : invalid calling object error

[gnutix]

Hello,

I unfortunately have to support IE9 in my application, and I noticed that users get an "invalid calling object" error at the line that ifvisible.js is loaded (here's the complete JS file : https://gist.github.com/gnutix/a419b8eb9019a3cb5429e91bc39a066b , look at line 33 ).

Would you know by any chance what part of the code would trigger this and if it's an easy fix ?

Thanks for your help.
gnutix