             return unless key? # wierd error
             return unless key.indexOf(@prefix) is 0
             return if key in useful
-            @del_content key, (error) =>
-                @logger.error(error) 
+            @del_content(key)
+                .catch (error) => @logger.error(error) 
             return
         return

        return localforage.setItem(key, content, cb)

    get_contents_keys: (cb) ->
        localforage.keys (err, keys) =>            
            return console.error(err) if err?
            for key in keys
                cb(key)
            return
        return

    del_content: (key, cb) ->


        module = queue.shift()
        key = @make_key(module)
        return @get_content(key)
            .then (module_source) =>

            unless module_source?
                @emit("EvaluationError", module, new NoSourceError(module.url))
