This is a very well-written piece and I really enjoyed reading Jorend's analysis of "Open" vs "Close" hash table performance [1] linked in the article. All fou

This is a very well-written piece and I really enjoyed reading Jorend's analysis of "Open" vs "Close" hash table performance [1] linked in the article. All four of these collection types are sorely needed in JS and will have many positive effects into the future. I am especially happy to have WeakSet, which virtually eliminates a number of pesky memory leak cases that happen all the time in DOM library code. ES has a bright future and it is great to see the committee making so many great choices while it grows. It is truly great that the community has not only been given significant opportunity to comment on and contribute to the spec, but to actually test code written with the new spec using transformers like Babel to ensure that they not only sound good, they work well in practice. What a breath of fresh air it is to evolve the web this way, rather than having a committee simply unilaterally define a specification (without a reference implementation) that turns out to be bug-prone, slow, or incomplete. 1. https://wiki.mozilla.org/User:Jorend/Deterministic_hash_tables https://wiki.mozilla.org/User:Jorend/Deterministic_hash_tabl...