Nullish Coalescing (Stage 3)

[hzoo]

Champions: @gisenberg
Spec Repo: https://github.com/gisenberg/proposal-nullary-coalescing
First presented at the July 2017 meeting: slides
Moved to Stage 1 at the Sept 2017 meeting: slides

Syntax

a ?? b

When performing optional property access in a nested structure in conjunction with the optional chaining operator, it is often desired to provide a default value if the result of that property access is null or undefined. At present, a typical way to express this intent in JavaScript is by using the || operator.

so most use const variable = a || b but a falsy value like 0 or '' or false will unintentionally return b as the value.

Notes:

While this proposal specifically calls out null and undefined values, the intent is to provide a complementary operator to the optional chaining operator. This proposal will update to match the semantics of that operator.

Parsing

• a new node type name (operator)?
• pluginName?

https://twitter.com/littledan/status/908032146484469761
https://github.com/babel/babylon/pull/742/files#r142008197

[jridgewell]

logicalCOALESCE? Too much of a mouthful? logicalQQ?

[gisenberg]

I started referring to this as the existential operator in the slides.

[hzoo]

@gisenberg feel free to edit the title/etc (if your in the tc39 team it gives you write access to this repo)

[ljharb]

(see tc39/proposal-nullish-coalescing#3)

[azz]

Parser PR: babel/babylon#761, follow-up: babel/babylon#762
Transform PR: babel/babel#6483

[vjpr]

What is the status of this? Is it ready to use?

[azz]

Yes, just enable the @babel/plugin-proposal-nullish-coalescing-operator plugin.

https://www.npmjs.com/package/@babel/plugin-proposal-nullish-coalescing-operator

[hzoo]

Yep https://github.com/babel/babel/tree/master/packages/babel-plugin-proposal-nullish-coalescing-operator