Turns out an array from a document rendered in IE’s Compatibility Mode doesn’t do Array.map(); … even when it’s used in a document that’s in normal IE 11 mode.
I found this out while integrating a legacy application with a modern application that opens in a second window and needs to be tossed a configuration object. Interestingly, we’re using ExtJS as our framework for the modern application in question, and the config handler uses Ext.Array.map(), which is meant to use a polyfill when Array.map() support is not there.
The problem? Ext.Array.map() tests an exemplar array of its own making, not the one it’s about to act on. Probably helpful for performance, but not what I needed in this case. Luckily, the array structure wasn’t super vital, as there was a deprecated way of specifying the same configs via several booleans instead. Lucky I didn’t clean those up yet.
Another fun day in legacy code…