I think this whole block could be shortened to one line:

```js
type = filter.getCallee().getName();
```

If the `filterMap_` were updated to use keys like the `ol.expr.functions` enum values (e.g. `fid`, `ieq`, `ineq`, `like`, etc.).

I also think I'd assert that the result of `filter.getCallee()` was an instance of `ol.expr.Identifier` before calling `getName`.