A binding pattern without rest element can have a trailing comma

[ikatyang]

TypeScript Version: 2.9.1/3.0.0-dev.20180602

Search Terms:

• trailing comma
• binding pattern
• A rest parameter or binding pattern may not have a trailing comma.

Code

declare const anything: any[];

let a;

[
  a,
] = anything;

let [
  b,
] = anything;

Expected behavior:
no error

Actual behavior:

test.ts:6:4 - error TS1013: A rest parameter or binding pattern may not have a trailing comma.

6   a,
     ~

Per ECMAScript Spec, the trailing comma is allowed in a binding pattern without rest element.

Playground Link:
link

Related Issues:

(from prettier/prettier#4624)

[mhegazy]

PRs welcomed.

declare const anything: any[];

let a;

[
a
] = anything;

let [
b,
] = anything;

[23:31:52] Found 0 errors. Watching for file changes.

Correct me if i wrong

[mhegazy]

thanks @alexandrLamdan1995

[bakkot]

@mhegazy I'm still seeing this on master:

$ cat in.ts
let a; [a,] = <any>[];

$ git rev-parse --short HEAD
7eaa78846e

$ gulp local
[...]

$ node built/local/tsc.js in.ts
in.ts:1:10 - error TS1013: A rest parameter or binding pattern may not have a trailing comma.

1 let a; [a,] = <any>[];
           ~

Looks like this was introduced in #22262. I'll submit a PR in a moment here.

[tarhunakau]

Will anyone try to fix it? Windows update - crash + BSOD, skype update - crash, Typescript update - crash. Do you have testers for your own products? The worst QA in all over the world... And that is Microsoft.

[j-f1]

It’ll be fixed by #24672 @BLRplex.