Feature:
* Show DevTools backend and frontend versions in UI (bvaughn in #23399)
* Timeline profiler refactored to support reading basic profiling data directly from React (bvaughn in #22529)

Bugfix:
* Better handle undefined Error stacks in DevTools error boundary (bvaughn in #24065)
* Fixed edge case bug in Profiler commit filtering (bvaughn in #24031)
* Gracefully handle empty "xstyle" prop values (lunaruan in #23279 and bvaughn in #23190)
* Add <TracingMarker> component boilerplate (lunaruan in #23275)

Misc:
* Remove object-assign polyfill (sebmarkbage in #23351)

### Feature
* DevTools: Only show StrictMode badge on root elements ([bvaughn](https://github.com/bvaughn) in [#23012](https://github.com/facebook/react/pull/23012))

#### Bugfix
* Don't crawl unmounted subtrees when profiling starts ([bvaughn](https://github.com/bvaughn) in [#23162](https://github.com/facebook/react/pull/23162))
* Filter deleted components from the updaters list to avoid runtime errors later ([lunaruan](https://github.com/lunaruan) in [#23156](https://github.com/facebook/react/pull/23156))

#### Misc
* DevTools (not React) logs Timeline performance data to the User Timing API ([bvaughn](https://github.com/bvaughn) in [#23102](https://github.com/facebook/react/pull/23102))

Features:
* Support multiple DevTools instances per page (@bvaughn in #22949)
* Advocate for StrictMode usage within Components tree (@bvaughn in #22886)
* StyleX plug-in for resolving atomic styles to values for props.xstyle (@bvaughn in #22808)
* Timeline search (@bvaughn in #22799)
* Add test selectors to experimental build (@bvaughn in #22760)
* Timeline: Improved snapshot view (@bvaughn in #22706)
* Display root type for root updates in "what caused this update?" (@eps1lon in #22599)
* Add open in editor for fb (@ezzak in #22649)

Bugfix:
* DevTools should inject itself for XHTML pages too (not just HTML) (@bvaughn in #22932)
* Don't restore profiling data if we're profling (@eps1lon in #22753)
* DevTools should properly report re-renders due to (use)context changes (@bvaughn in #22746)
* Filter empty commits (all Fibers bailed out) from Profiler (@bvaughn in #22745)
* Accept json file in import fileinput (@jyash97 in #22717)
* Expose css vars to reach-ui portal components (@jyash97 in #22716)
* Fix DevTools advanced tooltip display conditional check (@bvaughn in #22669)

Misc:
* Internally log errors occurring or reported to the frontend (@jstejada in #22948)
* Emit new event when DevTools connects in standalone app (@jstejada in #22848)
* DevTools: Log version in internal logger (@jstejada in #22825)
* Proof of Concept for E2E tests using playwright (@akgupta0777 in #22754)
* Add internal link to Scheduling Profiler (@bvaughn in #22730)

## 4.21.0 (October 31, 2021)

#### Features
* Scheduling Profiler: Add marks for component effects (mount and unmount) ([@bvaughn](https://github.com/bvaughn) in [#22578](https://github.com/facebook/react/pull/22578))
* Scheduling Profiler: De-emphasize React internal frames ([bvaughn](https://github.com/bvaughn) in [#22588](https://github.com/facebook/react/pull/22588))


#### Bugfix
* Revert logic for checking for duplicate installations of DevTools potentially causing issues loading Components tab ([@jstejada](https://github.com/jstejada) in [#22638](https://github.com/facebook/react/pull/22638))
* Scheduling Profiler does not warn about long transitions ([@bvaughn](https://github.com/bvaughn) in [#22614](https://github.com/facebook/react/pull/22614))
* Re-enable 'Reload and Start Profiling' for Microsoft Edge ([@eoandersson](https://github.com/eoandersson) in [#22631](https://github.com/facebook/react/pull/22631))


#### Misc
* DevTools supports ENV-injected version for better internal bug reports ([@bvaughn](https://github.com/bvaughn) in [#22635](https://github.com/facebook/react/pull/22635))
* Fix typos ([@KonstHardy](https://github.com/KonstHardy) in [#22494](https://github.com/facebook/react/pull/22494))

## 4.20.2 (October 20, 2021)

#### Bugfix
* Dev Tools: Relax constraint on passing extensionId for backend init ([@jstejada](https://github.com/jstejada) in [#22597](https://github.com/facebook/react/pull/22597))
* DevTools: Fix passing extensionId in evaled postMessage calls ([@jstejada](https://github.com/jstejada) in [#22590](https://github.com/facebook/react/pull/22590))

## 4.20.1 (October 19, 2021)

#### Bugfix
* Only show DevTools warning about unrecognized build in Chrome ([@jstejada](https://github.com/jstejada) in [#22571](https://github.com/facebook/react/pull/22571))
* DevTools: Include Edge in browser name detection ([@jstejada](https://github.com/jstejada) in [#22584](https://github.com/facebook/react/pull/22584))

## 4.20.0 (October 15, 2021)

#### Features
* Allow to use the Profiler when no client is connected in standalone DevTools ([@gabrieltrompiz](https://github.com/gabrieltrompiz) in [#22551](https://github.com/facebook/react/pull/22551))

#### Bugfix
* Surface backend errors during inspection in the frontend UI ([@bvaughn](https://github.com/bvaughn) in [#22546](https://github.com/facebook/react/pull/22546))
* Prevent splash page in standalone app from becoming unresponsive after the disconnection of a client (#22558) ([@gabrieltrompiz](https://github.com/gabrieltrompiz) in [#22560](https://github.com/facebook/react/pull/22560))
* Prevent errors/crashing when multiple installs of DevTools are present ([@jstejada](https://github.com/jstejada) in [#22517](https://github.com/facebook/react/pull/22517))
* Update Fiber logic in backend renderer to match implementation in React ([@jstejada](https://github.com/jstejada) in [#22527](https://github.com/facebook/react/pull/22527))

#### Misc
* Show warning in UI when duplicate installations of DevTools extension are detected ([@jstejada](https://github.com/jstejada) in [#22563](https://github.com/facebook/react/pull/22563))
* Improved filenames of built worker files ([@akgupta0777](https://github.com/akgupta0777) in [#22559](https://github.com/facebook/react/pull/22559))

Bugfix
* Show different error boundary UI for timeouts than normal errors (bvaughn in #22483)
* Fixed bug where deleting a component filter would also close the settings modal (Biki-das in #22484)

* Fixed potential cache miss when insepecting elements (https://github.com/facebook/react/pull/22472)

## 4.19.0 (September 29, 2021)

#### Features
* Scheduling Profiler: Show Suspense resource .displayName ([bvaughn](https://github.com/bvaughn) in [#22451](https://github.com/facebook/react/pull/22451))
* Scheduling Profiler marks should include thrown Errors ([bvaughn](https://github.com/bvaughn) in [#22419](https://github.com/facebook/react/pull/22419))
* Don't patch console during first render in strict mode ([lunaruan](https://github.com/lunaruan) in [#22308](https://github.com/facebook/react/pull/22308))
* Show which hook indicies changed when profiling for all builds ([bvaughn](https://github.com/bvaughn) in [#22365](https://github.com/facebook/react/pull/22365))
* Display actual ReactDOM API name in root type ([eps1lon](https://github.com/eps1lon) in [#22363](https://github.com/facebook/react/pull/22363))
* Add named hooks support to standalone and inline DevTools ([jstejada](https://github.com/jstejada) in [#22320](https://github.com/facebook/react/pull/22320) and [bvaughn](https://github.com/bvaughn) in [#22263](https://github.com/facebook/react/pull/22263))
#### Bugfix
* DevTools encoding supports multibyte characters (e.g. "🟩") ([bvaughn](https://github.com/bvaughn) in [#22424](https://github.com/facebook/react/pull/22424))
* Improve DEV errors if string coercion throws (Temporal.*, Symbol, etc.) ([justingrant](https://github.com/justingrant) in [#22064](https://github.com/facebook/react/pull/22064))
* Fix memory leak caused by not storing alternate Fiber pointer ([bvaughn](https://github.com/bvaughn) in [#22346](https://github.com/facebook/react/pull/22346))
* Fix call stack exceeded error in `utfDecodeString()` ([bvaughn](https://github.com/bvaughn) in [#22330](https://github.com/facebook/react/pull/22330))
* Fix runtime error when inspecting an element times out ([jstejada](https://github.com/jstejada) in [#22329](https://github.com/facebook/react/pull/22329))

#### Performance
* DevTools: Lazily parse indexed map sections ([bvaughn](https://github.com/bvaughn) in [#22415](https://github.com/facebook/react/pull/22415))
* DevTools: Hook names optimizations ([bvaughn](https://github.com/bvaughn) in [#22403](https://github.com/facebook/react/pull/22403))
* Replaced `network.onRequestFinished()` caching with `network.getHAR()` ([bvaughn](https://github.com/bvaughn) in [#22285](https://github.com/facebook/react/pull/22285))

## 4.18.0 (September 1, 2021)

#### Features
* DevTools: Improve named hooks network caching ([bvaughn](https://github.com/bvaughn) in [#22198](https://github.com/facebook/react/pull/22198))
* Console Logging for StrictMode Double Rendering ([lunaruan](https://github.com/lunaruan) in [#22030](https://github.com/facebook/react/pull/22030))

### Bugfix
* Fix react-devtools-inline size issues ([lunaruan](https://github.com/lunaruan) in [#22232](https://github.com/facebook/react/pull/22232))
* devtools: Don't display hook index of useContext ([eps1lon](https://github.com/eps1lon) in [#22200](https://github.com/facebook/react/pull/22200))
* Throw error in console without interfering with logs ([lunaruan](https://github.com/lunaruan) in [#22175](https://github.com/facebook/react/pull/22175))

Features
* Scheduling Profiler: Add network measures (bvaughn in #22112)
* Add options for disabling some features (hbenl in #22136)

Bugfix
* Fixed broken scroll-to error or warning feature (bvaughn and eps1lon in #22147 and #22144)
* Replaced WeakMap with LRU for inspected element cache (bvaughn in #22160)
* Add more detailed error handling if profiling data does not have any React marks (byronluk in #22157)
* Various named hooks bug fixes (jstejada in #22129, #22128, #22096, and #22148)
* Fix tooltip wheel event regression (bvaughn in #22130)
* Replace source-map library with source-map-js for named hooks source map parsing (bvaughn in #22126)

## 4.16.0 (August 16, 2021)
#### Features
* Scheduling Profiler: Inline snapshots ([bvaughn](https://github.com/bvaughn) in [#22091](https://github.com/facebook/react/pull/22091) and[bvaughn](https://github.com/bvaughn) in [#22088](https://github.com/facebook/react/pull/22088))
#### Bugfix
* split parsing code to unblock Firefox release ([lunaruan](https://github.com/lunaruan) in [#22102](https://github.com/facebook/react/pull/22102))
* Scheduling profiler: Canvas views clip by default ([bvaughn](https://github.com/bvaughn) in [#22100](https://github.com/facebook/react/pull/22100))
* Fixed Components tree indentation bug for Chrome extension ([bvaughn](https://github.com/bvaughn) in [#22083](https://github.com/facebook/react/pull/22083))

Features
* Display hook names for inspected components (saphal1998, VibhorCodecianGupta, bvaughn, and motiz88 in #21641, #21790, #21814, #21815, #21831, #21833, #21835, #21865, #21871, #21874, #21891)
* Control for manually toggling error boundaries (baopham in #21583)
* Allow user to manually enter Profiler commit number to jump between commits (srubin in #19957)

Bug fixes for Fast Refresh and DevTools interop.

# Install build tools
yarn && cd scripts/release && yarn install && cd ../../

# Download dependencies
scripts/release/download-experimental-build.js --build=319702

# Build extensions
cd packages/react-devtools-extensions && yarn build

Misc
* Updated react and react-dom API imports in preparation for upcoming stable release (bvaughn in #21488)

Bugfix
* Reload all roots after Fast Refresh force-remount (to avoid corrupted Store state) (bvaughn in #21516 and #21523)
* Errors thrown by Store can be dismissed so DevTools remain usable in many cases (bvaughn in #21520)
* Fixed string concatenation problem when a Symbol was logged to console.error or console.warn (bvaughn in #21521)
* DevTools: Fixed version range NPM syntax (bvaughn in 9cf1069)
* Tweaked DevTools error template title to match issue form template (bvaughn in 1a2d792)

* Improved bug report template to use new GitHub issue forms (bvaughn in #21450)

Bugfix
* Improve display name logic for React.memo components (bvaughn in #21392)
* Fixed potential runtime error with Suspense in versions <= 17 (bvaughn in #21432)
* Errors thrown in the Store are no longer silent (bvaughn in #21426)

Misc
* Improved bug report template (bvaughn in #21413), #21421)

Features
* Add Bridge protocol version backend/frontend (bvaughn in #21331)

Bugfix
* DevTools iterates over siblings during mount (rather than recursing) to avoid stack overflow errors (bvaughn in #21377)
* Multiple error dialogs can be visible at once (bvaughn in #21370)
* Console patching should handle Symbols without erroring (bvaughn in #21368)

#### Bugfix
* Wrapped quotation marks around Fiber ids or indices for all DevTools errors to better support GitHub fuzzy error search (@bvaughn in https://github.com/facebook/react/pull/21301)
* DevTools reliably suppresses console logs when generating component stacks (@bvaughn in https://github.com/facebook/react/pull/21301)
* Fixed `react-devtools-inline` bug in frontend `initialize` method (@bvaughn in https://github.com/facebook/react/pull/21265)

Bugfix
* $r should contain hooks property when it is forwardRef or memo component (meowtec in #20626)
* Ensure sync-xhr is allowed before reload and profile (ChrisDobby in #20879)
* Bump electron version from 9.1.0 to 11.1.0 for darwin-arm64 builds (jaiwanth-v in #20496)
* Fixed primitive hook badge colors for light theme (bvaughn in #21034)
* Increased minimum Chrome/Firefox versions from 51/54 to 60/55 to reduce polyfill code. (bvaughn in #21185)
* Fix can't expand prop value in some scenario (iChenLei in #20534)
* Flush updated passive warning/error info after delay (bvaughn in #20931)
* Patch console methods even when only show-inline-warnings/errors enabled (bvaughn in #20688)
* React Native fixes for new inline errors feature (bvaughn in #20502)
* Fixed invalid work tag constants that affected a certain range of React versions (bvaughn in #20362)

Features
* Improve Profiler commit-selector UX (bvaughn in #20943)
* Swap log with cbrt for commit bar height (bvaughn in #20952)
* Integrate with new experimental React Suspense features to improve props loading and inspection UX (bvaughn in #20548, #20789, #20458)
* Expose DEV-mode warnings in devtools UI (eps1lon in #20463)
* Display shortcuts for prev/next search result (eps1lon in #20470)
* Increase the clickable area of the prop value (TryingToImprove in #20428)

Experimental features
The following features are only enabled when used with (experimental) builds of React:
* Shows which fibers scheduled the current update (bvaughn in #21171)
* Add commit and post-commit durations to Profiler UI (bvaughn in #20984, #21183)
* Show which hooks (indices) changed when profiling (bvaughn in #20998)

Bugfixes:
* Fixed invalid internal work tag mappings (bvaughn) in (https://github.com/facebook/react/pull/20362)

#### Features
* Make DevTools Websocket retry delay configurable (@bvaughn - https://github.com/facebook/react/pull/20107)

#### Bugfix
* Fix error loading source maps for devtools extension (@sytranvn - https://github.com/facebook/react/pull/20079)
* Remove css sourcemap for `eact-devtools-inline (@sean9keenan - https://github.com/facebook/react/pull/20170)
* Decrease NPM update notification/prompt for standalone DevTools (@recurx - https://github.com/facebook/react/pull/20078)

#### Features
* Improved DevTools editing interface (@bvaughn - #19774)
* Add ⎇ + arrow key navigation (@bvaughn - #19741)
* Add checkbox toggle for boolean values (@mdaj06 - #19714)
* Show symbols used as keys in state (@omarsy - #19786)
* Add new (unstable) `SuspenseList` component type (@bpernick - #19684)

#### Bugfix
* Show proper icon/tooltip for restricted browser pages (@sktguha - #20023)
* Fix emoji character shown in Chrome developer tools panel (@bvaughn - #19603)
* Don't open two tabs in Firefox when clicking on troubleshooting instructions (@unbyte - #19632)
* Support inner component `_debugOwner` in memo (@bvaughn - #19556)
* Proxied methods should be safely dehydrated for display (@pfongkye))
* Property list values should show whitespace (@sammarks - #19640)
* Fix crash when inspecting document.all (@omarsy - #19619)
* Don't call generators during inspection since they may be stateful (@todortotev - #19831)
* Fix bad null check in DevTools highlight code (@bvaughn - #20010)
* Handled a missing suspense fiber when suspense is filtered on the profiler (@IDrissAitHafid)
* Fixed unfound node error when Suspense is filtered (@IDrissAitHafid - #20019)
* Always overrides the dispatcher when shallow rendering (@bvaughn - #20011)
* Frevent phishing attacks (@iamwilson - #19934)

### Other
* Enable source maps for DevTools production builds (@jpribyl - #19773)
* Drop support for IE 11 (@bvaughn - #19875)
* Remove ReactJS.org version check "cheat" (@sktguha - #19939)
* Update outdated links and fix two broken links (@sktguha - #19985)
* Remove support for deprecated/unreleased React Flare event system (@trueadm - #19520)