At the time of writing this blog post, optional chaining is reached stage4 in TC39 proposals and probably will be included in ES2020. Optional chaining is a new feature that can make your JavaScript code look more clear.

When you want to reach a property of an object, usually you can use && operator to avoid getting errors when the object is null or undefined.

const city = user && user.address && user.address.city;

With this new JavaScript feature this syntax become better and more clear than the one above.
You can just use ?. instead of adding && operator for each level of the tree.

Code above can be written as:

const city = user?.address?.city;

If user or address is undefined or null, then the value of city become undefined.
If you want to experiment this feature, you can use this Babel plugin.

Another new feature I liked is Nullish Coalescing feature. It is kind of a complementary feature for optional chaining and also planned to be released in ES2020.

You can also read this post in my blog.