In 2016, browsers were still working on implementing es2015 (I'm still waiting for proper tail calls on non-Safari engines). Atomics is a huge feature (especia

In 2016, browsers were still working on implementing es2015 (I'm still waiting for proper tail calls on non-Safari engines). Atomics is a huge feature (especially in the amount of work required). getOwnPropertyDescriptors is also a big addition. Async iteration is a very big deal that can potentially affect things like reading files in node. Object spread seems big, but is actually far more simple as it is a syntactic special case of Object.assign(). In contrast, the far reaching repercussions of adding async iteration and the implementation are both large things. Given the level of optimization for JS regex, adding a bunch of new features there is also a big job. Promise finally is also a big update (though combining map and flatmap in promises automatically is the biggest issue with them). This year, there's integers, working imports, and big class upgrades in the works. The list of major proposals is rapidly shrinking. Is there another major language adding that many big features in the past three years? Keep in mind that most stage 3 proposals already have at least one implementation already done.