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Emit destructuring patterns in 'for...in' statements for ES3/5 #2272

Closed as not planned
Closed as not planned
Emit destructuring patterns in 'for...in' statements for ES3/5#2272
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BugA bug in TypeScriptHelp WantedYou can do this
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@JsonFreeman
Jason Freeman (JsonFreeman)
opened on Mar 9, 2015

The following is allowed by the ES6 grammar:

for (var [a, b] in []) { }

This results in a type check error, because it doesn't make sense to destructure a string key. But it should still emit correctly downlevel. Right now we emit:

for (var _a = void 0, a = _a[0], b = _a[1] in []) { }

which is incorrect.

Activity

  1. Jason Freeman (JsonFreeman)
    added
    BugA bug in TypeScript
    on Mar 9, 2015

  2. mhegazy commented on Mar 10, 2015

    @mhegazy
    Mohamed Hegazy (mhegazy)
    on Mar 10, 2015
    Contributor

    so what is the proposed emit?

  3. JsonFreeman commented on Mar 10, 2015

    @JsonFreeman
    Jason Freeman (JsonFreeman)
    on Mar 10, 2015
    ContributorAuthor

    Similar to 'for...of', but 'for...in'-ified:

    for (var _a in []) {
    var a = _a[0], b = _a[1];
}
  4. Mohamed Hegazy (mhegazy)
    added
    Help WantedYou can do this
    on Mar 11, 2015
  5. Mohamed Hegazy (mhegazy)
    added this to the milestone on Mar 11, 2015
  6. Ryan Cavanaugh (RyanCavanaugh)
    modified the milestones: Community, Backlog on Mar 7, 2019

  7. RyanCavanaugh commented on Mar 1, 2024

    @RyanCavanaugh
    Ryan Cavanaugh (RyanCavanaugh)
    on Mar 1, 2024
    Member

    Doesn't seem like anyone has noticed this

  8. Ryan Cavanaugh (RyanCavanaugh)
    closed this as not plannedon Mar 1, 2024
  9. microsoft
    locked as resolved and limited conversation to collaborators on Oct 21, 2025
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