This JavaScript feature adds the capability for testing the existence of a private field in an object: "#foo in obj" Proposal: The feature has reached Stage 3 in TC39.


See proposal for motivating examples.


Specification link

Specification being incubated in a Community Group

Status in Chromium


Enabled by default (tracking bug)

Consensus & Standardization

After a feature ships in Chrome, the values listed here are not guaranteed to be up to date.

  • No signal
  • No signal
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Last updated on 2021-12-13