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Array filter on array does not correct types returned from map #35988

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Array filter on array does not correct types returned from map#35988
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Description

@alzalabany
Momen Zalabany (alzalabany)
opened on Jan 3, 2020

Search Terms:
Type Array filter

Code

type T = { id:number };
const obj = [{id:1},{id:2},{id:3}]
const ids = [1,2,5];
const error:T[] = ids.map(id=>obj[id] ? obj[id] : false).filter(Boolean);

Expected behavior:
const error should be T[] only;

Actual behavior:
// error type is T | false

Related Issues:
7657

Activity

  1. MartinJohns commented on Jan 4, 2020

    @MartinJohns
    Martin Johns (MartinJohns)
    on Jan 4, 2020
    Contributor

    Duplicate of #32834, #31164, #24063, #16655. Was implemented by #29955, and broken by #31515.

    Search terms used: filter boolean

  2. Ryan Cavanaugh (RyanCavanaugh)
    added
    DuplicateAn existing issue was already created
    on Jan 6, 2020
  3. TypeScript Bot (typescript-bot)
    closed this as completedon Jan 9, 2020

  4. typescript-bot commented on Jan 9, 2020

    @typescript-bot
    TypeScript Bot (typescript-bot)
    on Jan 9, 2020
    Contributor

    This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

  5. OmgImAlexis commented on May 12, 2020

    @OmgImAlexis
    Alexis Tyler (OmgImAlexis)
    on May 12, 2020

    Martin Johns (@MartinJohns) since this was broken by #31515 can we get a new issue open to track this? Otherwise you're just going to keep closing issues as duplicates.

  6. MartinJohns commented on May 12, 2020

    @MartinJohns
    Martin Johns (MartinJohns)
    on May 12, 2020
    Contributor

    Alexis Tyler (@OmgImAlexis) I'm not a member of the TypeScript team, so I have no say in this. But.. why get a new issue? There are existing issues about this, see my comment from before: #35988 (comment)

  7. OmgImAlexis commented on May 12, 2020

    @OmgImAlexis
    Alexis Tyler (OmgImAlexis)
    on May 12, 2020

    The first two issues you linked were closed, I had assumed the others were too.

  8. microsoft
    locked as resolved and limited conversation to collaborators on Oct 21, 2025
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