Epix not supporting arrays?

Someone reported that apparently one of my apps did not run on the Epix anymore. What had changed in my app was that I was searching inside an an array.

I could reduce the problem to two lines like these:
var arr = [1,2,3];
var idx =arr.indexOf(arr);

Insert this in any app, run them on any device should be fine, but on an Epix (also in the simulator) it throws an error "Could not find symbol indexOf". Same would happen if you use another array function like slice (although I did not try all array functions).