Time complexity of Set and Map in javascript

According to the ECMA documentation for Set and Maps (http://www.ecma-international.org/ecma-262/6.0/index.html#sec-set-objects):

Set objects must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structures used in this Set objects specification is only intended to describe the required observable semantics of Set objects. It is not intended to be a viable implementation model.

You will find similar sentences for Maps, WeakMaps and WeakSets. So, you should expect the time-complexity to be sublinear. Also, you can check out a solution on Javascript ES6 computational/time complexity of collections