Map and Set iterators are now way faster in V8, up to 11x (as per @bterlson's request) 

http://benediktmeurer.de/2017/07/14/faster-collection-iterators/ …pic.twitter.com/KOcO57PB5I
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Good question for @_gsathya 
Objects and collections will have the same backing store soon so they shouldn't be different
Strings don't undergo the hidden class transition when added to collections as they store the hash in an internal field
Specifically for iteration, collections are better (and have always been better) compared to dictionary objects.pic.twitter.com/ySLbqJPoA1
What about lookups?
That highly depends on the exact workload. Not so easy to put a general number by it. What I see is mostly dictionaries are still faster.
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