[""] is actually translated to . by the minifier, so it doesn't have any performance impact. In other words object.mySuperProperty will be minified to something like m.pX, but object["mySuperProperty"] will be minified to m.mySuperProperty (so it keeps the name but changes the syntax).
I just realised if 'Playtomic' is defined by an external script, you don't need to do what I said, because it's defined in another script that is not minified :)