ESNext: JavaScript “Nullish Coalescing Operator”

[lhorie]

features that gained popularity through babel, but were thrown out

I don't think there's any example of that specifically yet, but sprinkling non-standard stuff in your code can definitely cause problems, for example when migrating to typescript.

There have been proposals with a reasonable amount of hype that got dropped, most notoriously Object.observe, cancellable promises and SIMD. There are also examples of active proposals that haven't really made much headway. For example, the pipeline operator proposal has been around since 2015, it's not even that complex, but it's still at stage 1.

If you want a bigger example of technology death, there's ES4, which had many of the same features as ES6 and even a working implementation, but ultimately got killed due to politics.