I need an upload form field that may or may not allow the user to select more than one file.
I know I can do something like:
You can use ngSwitch directive for this. Take a look in AngularJs documentation for more details.
https://docs.angularjs.org/api/ng/directive/ngSwitch
In this demo example the directive switch between input file with and without multiple based in a scope param passed for directive using ngSwitch directive.
Demo using ngSwitch