@babel/plugin-transform-duplicate-keys

What is @babel/plugin-transform-duplicate-keys?

The @babel/plugin-transform-duplicate-keys npm package is designed to help developers manage object literals in JavaScript that have duplicate keys. When using this plugin, Babel will transform object literals containing duplicate keys by ensuring that the last key-value pair is the one that is ultimately defined, following the standard JavaScript behavior. This can be particularly useful in scenarios where code is being generated or transformed and duplicate keys may be introduced unintentionally.

What are @babel/plugin-transform-duplicate-keys's main functionalities?

Transforming Duplicate Keys in Object Literals

This feature allows the transformation of object literals with duplicate keys in JavaScript code. The plugin ensures that if an object literal contains duplicate keys, only the last occurrence of the key is kept, and previous ones are ignored. This aligns with the standard JavaScript behavior where the last property assignment overrides earlier assignments with the same key.

{"type": "object", "properties": {"duplicateKey": {"type": "string"}, "duplicateKey": {"type": "number"}}}

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README

@babel/plugin-transform-duplicate-keys

Compile objects with duplicate keys to valid strict ES5

See our website @babel/plugin-transform-duplicate-keys for more information.

Install

Using npm:

npm install --save-dev @babel/plugin-transform-duplicate-keys

or using yarn:

yarn add @babel/plugin-transform-duplicate-keys --dev

Changelog

v7.25.9 (2024-10-22)

:bug: Bug Fix

• babel-parser, babel-template, babel-types
  • #16905 fix: Keep type annotations in syntacticPlaceholders mode (@liuxingbaoyu)
• babel-helper-compilation-targets, babel-preset-env
  • #16907 fix: support BROWSERSLIST{,_CONFIG} env (@JLHwung)
• Other
  • #16884 Analyze ClassAccessorProperty to prevent the no-undef rule (@victorenator)

:house: Internal

• babel-helper-transform-fixture-test-runner
  • #16914 remove test options flaky (@JLHwung)

:running_woman: Performance

• babel-parser, babel-types
  • #16918 perf: Make VISITOR_KEYS etc. faster to access (@liuxingbaoyu)