ECMAScript 2019: the final feature set

Update 2019-01-29: The feature set of ECMAScript 2019 is now final (source) and described in this blog post.

A word on ECMAScript versions  #

Note that since the TC39 process was instituted, the importance of ECMAScript versions has much decreased. What really matters now is what stage a proposed feature is in: Once it has reached stage 4, it can be used safely. But even then, you still have to check if your engines of choice support it.

The features of ES2019  #

Major new features:

• Array.prototype.{flat,flatMap} (Michael Ficarra, Brian Terlson, Mathias Bynens)
• Object.fromEntries (Darien Maillet Valentine)

Minor new features:

• String.prototype.{trimStart,trimEnd} (Sebastian Markbåge)
• Symbol.prototype.description (Michael Ficarra)
• Optional catch binding (Michael Ficarra)
• Array.prototype.sort() is now required to be stable (ECMAScript spec) (Mathias Bynens).

Changes that are mostly internal:

• Well-formed JSON.stringify (Richard Gibson)
• JSON superset (Richard Gibson)
• Function.prototype.toString revision (Michael Ficarra)

Quoting @v8js on Twitter:

As of V8 v7.3 / Chrome 73, all of these ES2019 features are available by default. Enjoy!

FAQ  #

What do the stages mean?  #

They refer to maturity stages of the so-called “TC39 process”. Check chapter “The TC39 process for ECMAScript features” in “Exploring ES2016 and ES2017” for more information.

How is [my favorite proposed feature] doing?  #

If you are wondering what stages various proposed features are in, consult the readme of the ECMA-262 GitHub repository.

Is there an official list of ECMAScript features?  #

Yes, the TC39 repo lists finished proposals and mentions in which ECMAScript versions they are introduced.

Further reading  #

The following books of mine are free to read online:

• ECMAScript 5: “Speaking JavaScript”
• ECMAScript 6: “Exploring ES6”
• ECMAScript 2016 & 2017: “Exploring ES2016 and ES2017”
• ECMAScript 2018 & 2019: “Exploring ES2018 and ES2019”