Make this enum numeric instead - numeric enums are almost always better as they minify better (no need to embed 'bottom' in the compiled javascript when 0 will do) and are faster (switching on an integer is orders of magnitude faster than doing string comparisons). Event type names are usually the exception because they have to be unique, and sometimes enums exposed to external javascript are better as strings because then people writing code against the API in non-Closure javascript don't have to remember 'bottom is 0' and can just pass 'bottom', but in this case that's not needed.