arg: Extract variable
arg: Extract variable

This is for readability and saves a few calls of val.toObject(). It will
become convenient when we root the return value of toObject().

https://bugzilla.gnome.org/show_bug.cgi?id=742249

endlessm/gjs,endlessm/gjs,endlessm/gjs,endlessm/gjs,endlessm/gjs