--- title: "happy-dom Breaking Changes on npm | Since.dev" description: "What each happy-dom release removed, renamed or changed: 13,444 breaking changes in 30 versions on npm, each with its source." canonical_url: https://since.dev/packages/npm/happy-dom last_updated: 2026-10-20 --- # happy-dom breaking changes Every breaking API change we have recorded in happy-dom on npm: 13,444 breaking changes in 30 versions. Below are its newest 6 versions, removals and renames first, each with its source. Newest change October 20, 2026 ## 21.0.4 429 breaking changes, first published October 20, 2026. - **Removed** `AbortController.__@window@3465511` AbortController.\_\_@window@3465511 was removed in happy-dom 21.0.4 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.4) - **Removed** `AbortSignal.__@aborted@3465527` AbortSignal.\_\_@aborted@3465527 was removed in happy-dom 21.0.4 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.4) - **Removed** `AbortSignal.__@reason@3465529` AbortSignal.\_\_@reason@3465529 was removed in happy-dom 21.0.4 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.4) - **Removed** `Animation.__@propertyEventListeners@3465587` Animation.\_\_@propertyEventListeners@3465587 was removed in happy-dom 21.0.4 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.4) - **Removed** `Attr.__@affectsCache@3465736` Attr.\_\_@affectsCache@3465736 was removed in happy-dom 21.0.4 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.4) - **Removed** `Attr.__@assignedToSlot@3465732` Attr.\_\_@assignedToSlot@3465732 was removed in happy-dom 21.0.4 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.4) - **Removed** `Attr.__@cache@3465734` Attr.\_\_@cache@3465734 was removed in happy-dom 21.0.4 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.4) - **Removed** `Attr.__@childNodes@3465730` Attr.\_\_@childNodes@3465730 was removed in happy-dom 21.0.4 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.4) - **Removed** `Attr.__@clearCache@3465757` Attr.\_\_@clearCache@3465757 was removed in happy-dom 21.0.4 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.4) - **Removed** `Attr.__@connectedToDocument@3465763` Attr.\_\_@connectedToDocument@3465763 was removed in happy-dom 21.0.4 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.4) And 419 more in this version. ## 21.0.3 427 breaking changes, first published October 15, 2026. - **Removed** `AbortController.__@window@3482173` AbortController.\_\_@window@3482173 was removed in happy-dom 21.0.3 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.3) - **Removed** `AbortSignal.__@aborted@3482189` AbortSignal.\_\_@aborted@3482189 was removed in happy-dom 21.0.3 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.3) - **Removed** `AbortSignal.__@reason@3482191` AbortSignal.\_\_@reason@3482191 was removed in happy-dom 21.0.3 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.3) - **Removed** `Animation.__@propertyEventListeners@3482249` Animation.\_\_@propertyEventListeners@3482249 was removed in happy-dom 21.0.3 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.3) - **Removed** `Attr.__@affectsCache@3482398` Attr.\_\_@affectsCache@3482398 was removed in happy-dom 21.0.3 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.3) - **Removed** `Attr.__@assignedToSlot@3482394` Attr.\_\_@assignedToSlot@3482394 was removed in happy-dom 21.0.3 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.3) - **Removed** `Attr.__@cache@3482396` Attr.\_\_@cache@3482396 was removed in happy-dom 21.0.3 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.3) - **Removed** `Attr.__@childNodes@3482392` Attr.\_\_@childNodes@3482392 was removed in happy-dom 21.0.3 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.3) - **Removed** `Attr.__@clearCache@3482419` Attr.\_\_@clearCache@3482419 was removed in happy-dom 21.0.3 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.3) - **Removed** `Attr.__@connectedToDocument@3482425` Attr.\_\_@connectedToDocument@3482425 was removed in happy-dom 21.0.3 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.3) And 417 more in this version. ## 21.0.2 426 breaking changes, first published October 15, 2026. - **Removed** `AbortController.__@window@3498819` AbortController.\_\_@window@3498819 was removed in happy-dom 21.0.2 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.2) - **Removed** `AbortSignal.__@aborted@3498835` AbortSignal.\_\_@aborted@3498835 was removed in happy-dom 21.0.2 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.2) - **Removed** `AbortSignal.__@reason@3498837` AbortSignal.\_\_@reason@3498837 was removed in happy-dom 21.0.2 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.2) - **Removed** `Animation.__@propertyEventListeners@3498895` Animation.\_\_@propertyEventListeners@3498895 was removed in happy-dom 21.0.2 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.2) - **Removed** `Attr.__@affectsCache@3499044` Attr.\_\_@affectsCache@3499044 was removed in happy-dom 21.0.2 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.2) - **Removed** `Attr.__@assignedToSlot@3499040` Attr.\_\_@assignedToSlot@3499040 was removed in happy-dom 21.0.2 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.2) - **Removed** `Attr.__@cache@3499042` Attr.\_\_@cache@3499042 was removed in happy-dom 21.0.2 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.2) - **Removed** `Attr.__@childNodes@3499038` Attr.\_\_@childNodes@3499038 was removed in happy-dom 21.0.2 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.2) - **Removed** `Attr.__@clearCache@3499065` Attr.\_\_@clearCache@3499065 was removed in happy-dom 21.0.2 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.2) - **Removed** `Attr.__@connectedToDocument@3499071` Attr.\_\_@connectedToDocument@3499071 was removed in happy-dom 21.0.2 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.2) And 416 more in this version. ## 21.0.1 426 breaking changes, first published October 12, 2026. - **Removed** `AbortController.__@window@3515465` AbortController.\_\_@window@3515465 was removed in happy-dom 21.0.1 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.1) - **Removed** `AbortSignal.__@aborted@3515481` AbortSignal.\_\_@aborted@3515481 was removed in happy-dom 21.0.1 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.1) - **Removed** `AbortSignal.__@reason@3515483` AbortSignal.\_\_@reason@3515483 was removed in happy-dom 21.0.1 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.1) - **Removed** `Animation.__@propertyEventListeners@3515541` Animation.\_\_@propertyEventListeners@3515541 was removed in happy-dom 21.0.1 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.1) - **Removed** `Attr.__@affectsCache@3515690` Attr.\_\_@affectsCache@3515690 was removed in happy-dom 21.0.1 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.1) - **Removed** `Attr.__@assignedToSlot@3515686` Attr.\_\_@assignedToSlot@3515686 was removed in happy-dom 21.0.1 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.1) - **Removed** `Attr.__@cache@3515688` Attr.\_\_@cache@3515688 was removed in happy-dom 21.0.1 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.1) - **Removed** `Attr.__@childNodes@3515684` Attr.\_\_@childNodes@3515684 was removed in happy-dom 21.0.1 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.1) - **Removed** `Attr.__@clearCache@3515711` Attr.\_\_@clearCache@3515711 was removed in happy-dom 21.0.1 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.1) - **Removed** `Attr.__@connectedToDocument@3515717` Attr.\_\_@connectedToDocument@3515717 was removed in happy-dom 21.0.1 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.1) And 416 more in this version. ## 21.0.0 428 breaking changes, first published October 11, 2026. - **Removed** `AbortController.__@window@2742649` AbortController.\_\_@window@2742649 was removed in happy-dom 21.0.0 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.0) - **Removed** `AbortSignal.__@aborted@2742665` AbortSignal.\_\_@aborted@2742665 was removed in happy-dom 21.0.0 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.0) - **Removed** `AbortSignal.__@reason@2742667` AbortSignal.\_\_@reason@2742667 was removed in happy-dom 21.0.0 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.0) - **Removed** `Animation.__@propertyEventListeners@2742725` Animation.\_\_@propertyEventListeners@2742725 was removed in happy-dom 21.0.0 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.0) - **Removed** `Attr.__@affectsCache@2742874` Attr.\_\_@affectsCache@2742874 was removed in happy-dom 21.0.0 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.0) - **Removed** `Attr.__@assignedToSlot@2742870` Attr.\_\_@assignedToSlot@2742870 was removed in happy-dom 21.0.0 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.0) - **Removed** `Attr.__@cache@2742872` Attr.\_\_@cache@2742872 was removed in happy-dom 21.0.0 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.0) - **Removed** `Attr.__@childNodes@2742868` Attr.\_\_@childNodes@2742868 was removed in happy-dom 21.0.0 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.0) - **Removed** `Attr.__@clearCache@2742895` Attr.\_\_@clearCache@2742895 was removed in happy-dom 21.0.0 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.0) - **Removed** `Attr.__@connectedToDocument@2742901` Attr.\_\_@connectedToDocument@2742901 was removed in happy-dom 21.0.0 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/21.0.0) And 418 more in this version. ## 20.14.6 426 breaking changes, first published October 8, 2026. - **Removed** `AbortController.__@window@3580263` AbortController.\_\_@window@3580263 was removed in happy-dom 20.14.6 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/20.14.6) - **Removed** `AbortSignal.__@aborted@3580279` AbortSignal.\_\_@aborted@3580279 was removed in happy-dom 20.14.6 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/20.14.6) - **Removed** `AbortSignal.__@reason@3580281` AbortSignal.\_\_@reason@3580281 was removed in happy-dom 20.14.6 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/20.14.6) - **Removed** `Animation.__@propertyEventListeners@3580339` Animation.\_\_@propertyEventListeners@3580339 was removed in happy-dom 20.14.6 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/20.14.6) - **Removed** `Attr.__@affectsCache@3580488` Attr.\_\_@affectsCache@3580488 was removed in happy-dom 20.14.6 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/20.14.6) - **Removed** `Attr.__@assignedToSlot@3580484` Attr.\_\_@assignedToSlot@3580484 was removed in happy-dom 20.14.6 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/20.14.6) - **Removed** `Attr.__@cache@3580486` Attr.\_\_@cache@3580486 was removed in happy-dom 20.14.6 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/20.14.6) - **Removed** `Attr.__@childNodes@3580482` Attr.\_\_@childNodes@3580482 was removed in happy-dom 20.14.6 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/20.14.6) - **Removed** `Attr.__@clearCache@3580509` Attr.\_\_@clearCache@3580509 was removed in happy-dom 20.14.6 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/20.14.6) - **Removed** `Attr.__@connectedToDocument@3580515` Attr.\_\_@connectedToDocument@3580515 was removed in happy-dom 20.14.6 [npmjs.com](https://www.npmjs.com/package/happy-dom/v/20.14.6) And 416 more in this version. ## Check your code These are the changes. To see which of them reach your code, [scan a public repository](https://since.dev/scan.md), or have your coding agent call `check_code` with your manifest or lockfile over [MCP](https://since.dev/docs.md#mcp). [The API](https://since.dev/docs.md#api) reads every change in every version, not only the newest. A fix pull request opens for the changes that reach a connected repository. Nothing merges or deploys. ## Put your code on continuous maintenance. Scan a public repository now, or give your agent one line. [Scan a repository](https://since.dev/scan.md). Any public GitHub repository. No sign-in. ### Tell your agent what changed since it was trained. `claude mcp add --transport http since https://api.since.dev/mcp` [Get an API key](https://app.since.dev/login?mode=signup) Codex, Cursor and any MCP client use https://api.since.dev/mcp. --- Every page on this site as Markdown: https://since.dev/sitemap.md. For agents: https://since.dev/llms.txt.