1566143 - Implement the Optional Chaining operator (?.) proposal

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P3)

Description

[Alexandre Folle de Menezes]

The proposal is currently on Stage 2.

Comment 1

[Steven DeTar [:sdetar]]

This is being set as a P3 like other Stage 2 proposals

Comment 2

[Igor]

This proposal has been promoted to Stage 3

Comment 3

[Julien G]

Changing "Blocks" to Stage 3 per https://github.com/tc39/proposals/commit/25f8d6a4db03bcdd2cfd49bf32e312ce80e1c80e

Comment 4

[Sergey Rubanov]

It's implemented in both V8 and JSC now

Comment 5

[Yulia Startsev]

Attachment: Bug 1566143 - [WIP] implement optional chaining in the frontend

Comment 6

[Yulia Startsev]

Attachment: Bug 1566143 - [WIP] implement optional chaining in the frontend

Comment 7

[Alexandre Folle de Menezes]

The proposal is now on Stage 4.

Comment 8

[Yulia Startsev]

Attachment: Bug 1566143 - refactor coordnode

Comment 9

[Yulia Startsev]

Attachment: Bug 1566143 - Update parser for optional chaining

Depends on D58973

Comment 10

[Yulia Startsev]

Attachment: Bug 1566143 - Add Bytecode for Optional Property Access and Optional Element Access.

Depends on D58974

Comment 11

[Yulia Startsev]

Attachment: Bug 1566143 - Add parsing and Bytecode for deleting properties on an optional chain.

Depends on D58975

Comment 12

[Yulia Startsev]

Attachment: Bug 1566143 - Add bytecode for Optional Chain function calls.

Depends on D58976

Comment 13

[Yulia Startsev]

Attachment: Bug 1566143 - Add tests for Optional Chaining

Depends on D58977

Comment 14

[Yulia Startsev]

Attachment: Bug 1566143 - Add Bytecode for Optional Chaining;

Depends on D58974

Comment 15

[Yulia Startsev]

Attachment: Bug 1566143 - Add tests for Optional Chaining

Depends on D59869

Comment 16

[Daniel Varga [:dvarga]]

https://hg.mozilla.org/mozilla-central/rev/37071f53b00b
https://hg.mozilla.org/mozilla-central/rev/35b55a5b0e4d
https://hg.mozilla.org/mozilla-central/rev/254be9b0aaee
https://hg.mozilla.org/mozilla-central/rev/5d3392ccb733

Comment 17

[Nicolas Chevobbe [:nchevobbe]]

Yulia, as I started working on Bug 1594009 for console support, I wanted to check with you if it's normal for

document?.location?["origin"];

to throw a SyntaxError ? Chrome does the same, but in https://tc39.es/proposal-optional-chaining/ there are a few places where it looks like it should be possible? (I'm really not used to read specs, so I definitely can be wrong).

Comment 18

[Yulia Startsev]

Hi Nicolas,

Unfortunately, we can't use location?["origin"] because we cannot distinguish it from a ternary without a look ahead larger than one or two characters. the engine, when it sees a bare ?, it expects a ternary operator -> location ? ["origin"] : ..., which is what the syntax error refers to.

As a result, the committee settled on this syntax -> location?.["origin"] -- it isn't ideal, but it resolves the lookahead problem. if we didn't do it right away, we would have potential errors with automatic semicolon insertion, thus making it impossible for us to include it later due to web compat.

The same is true for function calls.

So, tl;dr-> yes, it should be a syntax error specifically for an incomplete ternary expression.

Comment 19

[Nicolas Chevobbe [:nchevobbe]]

(In reply to Yulia Startsev [:yulia] from comment #18)

So, tl;dr-> yes, it should be a syntax error specifically for an incomplete ternary expression.

Thanks a lot for the explanation :)

Comment 20

[Florian Scholz (Open Web Docs)]

Release notes: https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/74#JavaScript
Reference docs: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining