Now in Chrome, you can enable ES Harmony features.
Based on the v8 source ( we get proxies, weak maps, sets, maps, typeof semantics, and block scoping with this flag.
A new flag named Enable Experimental JavaScript appeared in the chrome://flags page of the last Chromium build. This flag enables web pages to use experimental JavaScript features.

And by that, it means Javascript Harmony also known as ECMAScript Harmony project. Read more:

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