[$250] Upgrade to ESLint 10

[roryabraham]

Problem

We are using an outdated version of ESLint. This means we're missing out on bug fixes and improvements and potentially making future upgrades harder.

Solution

Let's upgrade eslint-config-expensify, E/App, and react-native-onyx to ESLint 10.

Upwork Automation - Do Not Edit

• Upwork Job URL: https://www.upwork.com/jobs/~022027777699504561836
• Upwork Job ID: 2027777699504561836
• Last Price Increase: 2026-02-28

[melvin-bot]

Triggered auto assignment to Contributor-plus team member for initial proposal review - @suneox (External)

[melvin-bot]

Triggered auto assignment to @mallenexpensify (Bug), see https://stackoverflow.com/c/expensify/questions/14418 for more details. Please add this bug to a GH project, as outlined in the SO.

[melvin-bot]

Job added to Upwork: https://www.upwork.com/jobs/~022027777699504561836

[samranahm]

I previously Upgrade ESLint from v8 to v9 and eslint-config-expensify from 2.0.81 to 2.0.102 to enable eslint-plugin-unicorn performance rules here. I am open to take this.

cc: @roryabraham

[MelvinBot]

🔍 Issue Analysis

Please re-state the problem that we are trying to solve in this issue.

Expensify/App currently uses ESLint ^9.36.0 (installed: 9.36.0). ESLint 10.0.0 was released on February 6, 2026 with significant improvements and breaking changes. Staying on ESLint 9 means missing bug fixes, new rule capabilities (like JSX reference tracking), and makes future upgrades harder as the ecosystem moves forward.

The upgrade scope spans three repositories: eslint-config-expensify, Expensify/App, and react-native-onyx.

What is the root cause of that problem?

ESLint 10 introduces ~15 breaking changes versus ESLint 9. The most impactful for this codebase are:

1. eslintrc config system fully removed — The legacy .eslintrc format that was deprecated in v9 is completely gone. Any plugin/config still using legacy format must go through FlatCompat (from @eslint/eslintrc) or be updated natively.

2. Deprecated rule context methods removed — context.getFilename(), context.getCwd(), context.getSourceCode(), context.parserOptions are removed. Plugins using these will crash. This affects eslint-plugin-react and eslint-plugin-import in the current setup.

3. Deprecated SourceCode methods removed — getTokenOrCommentBefore(), getTokenOrCommentAfter(), isSpaceBetweenTokens(), getJSDocComment() are gone.

4. Node.js minimum raised to ^20.19.0, ^22.13.0, or >=24.

5. Config lookup changed — ESLint 10 locates eslint.config.* starting from the linted file's directory, not the CWD. The v10_config_lookup_from_file feature flag is removed.

6. eslint-env comments now errors — Any /* eslint-env */ comments in source files will be reported as lint errors.

7. JSX reference tracking enabled — <Component> usage now counts as a variable reference, fixing false positives in no-unused-vars but potentially surfacing new no-undef errors.

What changes do you think we should make in order to solve the problem?

The upgrade should be done in three phases, with eslint-config-expensify going first since both App and Onyx depend on it.

Phase 1: Upgrade eslint-config-expensify

• Bump eslint dependency from ^9.36.0 to >=9.36.0 <11 (or ^9.36.0 || ^10.0.0) in package.json
• Replace eslint-plugin-es v4.1.0 (deprecated/unmaintained) with eslint-plugin-es-x (actively maintained community fork, ESLint 10 compatible)
  • Update rule references: es/no-nullish-coalescing-operators → es-x/no-nullish-coalescing-operators, etc.
• Fix eslint-plugin-import compatibility — either update to an ESLint 10-compatible version or wrap with @eslint/compat's fixupPluginRules() (the plugin uses removed context.getFilename())
• Fix eslint-plugin-react compatibility — same approach as import plugin (uses removed context.getFilename())
• Evaluate replacing eslint-plugin-rulesdir v0.2.2 with ESLint 10's recommended inline virtual plugin pattern for custom Expensify rules
• Publish a new version of eslint-config-expensify with these changes

Phase 2: Upgrade Expensify/App

• Update eslint from ^9.36.0 to ^10.0.0 in package.json
• Update eslint-config-expensify to the new version from Phase 1
• Update @eslint/eslintrc to latest version (required for FlatCompat compatibility with ESLint 10)
• Address the 6 configs currently wrapped by FlatCompat in eslint.config.mjs:177-184:
  • airbnb-typescript — This is the biggest blocker. eslint-config-airbnb-typescript v18 uses legacy CJS module.exports, string-based plugins: ['@typescript-eslint'], and the legacy overrides pattern. It is also shimmed via npm overrides (eslint-config-airbnb-base aliased to eslint-config-expensify@2.0.91). Consider inlining the ~50 TypeScript rule overrides directly instead of depending on this unmaintained package.
  • prettier — eslint-config-prettier v9 should work through FlatCompat, or can be trivially replaced with its flat config export.
  • storybook — eslint-plugin-storybook v10.1.10 likely has flat config support natively.
  • react-native-a11y, @dword-design/import-alias, you-dont-need-lodash-underscore — Check for flat config exports; if not available, continue using FlatCompat.
• Update npm overrides section for ESLint 10 version ranges
• Remove any /* eslint-env */ comments from source files if present
• Remove v10_config_lookup_from_file flag if used anywhere
• Verify the --concurrency=auto CLI flag in the lint script still works
• Run linting and fix any new violations from JSX reference tracking and updated eslint:recommended

Phase 3: Upgrade react-native-onyx

• Bump eslint from ^9.39.2 to include ^10.0.0
• Update eslint-config-expensify to the new version from Phase 1
• Replace or remove @react-native-community/eslint-config v3.2.0 (legacy eslintrc format, incompatible with ESLint 10 without FlatCompat)

What alternative solutions did you explore?

• Wait for all plugin authors to update — Not viable, some plugins like eslint-config-airbnb-typescript appear unmaintained. Active workarounds are needed.
• Use @eslint/compat fixupPluginRules() as a blanket fix — This can temporarily patch plugins that use removed context methods (eslint-plugin-react, eslint-plugin-import), but it's better to use properly updated versions where available.
• Replace eslint-plugin-import with eslint-plugin-import-x — This is a maintained fork with native ESLint 10 support. However, it changes rule names, which adds migration effort. Worth evaluating for a cleaner long-term solution.

Detailed Investigation

Current State of the Codebase

App's ESLint setup (eslint.config.mjs, 645 lines):

• Uses ESLint 9's defineConfig() from eslint/config and globalIgnores() — this is the modern flat config format
• Config has a layered structure: eslint-config-expensify → typescript-eslint type-checked configs → file-progress plugin → react-compiler-compat processor → FlatCompat bridge for 6 legacy configs → direct plugin registrations → file-specific overrides → globalIgnores
• Lint script: NODE_OPTIONS=--max_old_space_size=8192 eslint . --max-warnings=383 --cache --cache-location=node_modules/.cache/eslint --cache-strategy content --concurrency=auto

eslint-config-expensify v2.0.105:

• Already uses flat config format with defineConfig() and ESM exports ✅
• Has eslint: "^9.36.0" as a direct dependency (not peer dep) — version range won't match ESLint 10
• Depends on deprecated eslint-plugin-es v4.1.0 and eslint-plugin-rulesdir v0.2.2
• Contains ~50 deprecated formatting rules in rules/base/style.js (still work in v10, removed in v11)

Plugin Compatibility Matrix:

Plugin	Version	Flat Config?	ESLint 10 Ready?
eslint-config-expensify	2.0.105	✅ Native	⚠️ Needs version bump + plugin fixes
typescript-eslint	^8.45.0	✅ Native	✅ Yes (v8.54+ required for ESLint 10)
eslint-plugin-react-hooks	^7.0.1	✅ Native	✅ Yes
eslint-plugin-react	^7.37.5	✅ Native	❌ Uses removed context.getFilename()
eslint-plugin-import	^2.32.0	✅ Native	❌ Uses removed context methods
eslint-plugin-jsdoc	^60.7.0	✅ Native	✅ Likely
eslint-plugin-unicorn	^61.0.2	✅ Native	✅ Likely
eslint-plugin-file-progress	3.0.1	✅ Native	✅ Yes
eslint-config-airbnb-typescript	18.0.0	❌ Legacy CJS	❌ Needs FlatCompat + major workarounds
eslint-plugin-es	4.1.0	❌ Legacy	❌ Deprecated, replace with eslint-plugin-es-x
eslint-plugin-rulesdir	0.2.2	❓ Unknown	⚠️ May work but unmaintained
eslint-config-prettier	^9.1.0	Via FlatCompat	✅ Trivial
eslint-plugin-storybook	^10.1.10	Via FlatCompat	✅ Likely has flat config
eslint-plugin-lodash	^7.4.0	Direct	⚠️ Unknown

ESLint 10 Breaking Changes Summary

Category	Change	Impact on This Codebase
Runtime	Node.js >= v20.19.0	Verify CI runners
Config	eslintrc completely removed	FlatCompat still works (must upgrade @eslint/eslintrc)
Config	Config lookup from file, not CWD	May affect monorepo lint behavior
Config	eslint-env comments are errors	Search for and remove any such comments
API	Deprecated context methods removed	Breaks eslint-plugin-react, eslint-plugin-import
API	Deprecated SourceCode methods removed	May break older plugins
Behavior	JSX references now tracked	May fix false positives but could surface new errors
CLI	eslintrc-specific flags removed	No impact (already using flat config)
Rules	eslint:recommended updated	Review for new rule violations

---

Next Steps for Contributor+ team: Reply with @MelvinBot implement this to create a draft PR, or @MelvinBot <your feedback> to refine this analysis.

[abbasifaizan70]

Proposal

Please re-state the problem that we are trying to solve in this issue.

We are using an outdated version of ESLint (v9). This means we're missing out on bug fixes and improvements (such as proper JSX reference tracking, updated eslint:recommended rules, and the new file-based config lookup algorithm) and potentially making future upgrades harder as the gap between our version and latest widens.

What is the root cause of that problem?

All three repositories (eslint-config-expensify, E/App, react-native-onyx) currently pin ESLint to ^9.x and several custom rules in eslint-config-expensify use deprecated context APIs that were removed in ESLint 10.

eslint-config-expensify declares eslint: ^9.36.0 in its dependencies:

https://github.com/Expensify/eslint-config-expensify/blob/16cef2c029311c6b3c25a83a730409d49493c766/package.json#L15

Six custom rules use context.getFilename() which was removed in ESLint 10 (replaced by context.filename):

https://github.com/Expensify/eslint-config-expensify/blob/16cef2c029311c6b3c25a83a730409d49493c766/eslint-plugin-expensify/no-api-in-views.js#L8-L13

https://github.com/Expensify/eslint-config-expensify/blob/16cef2c029311c6b3c25a83a730409d49493c766/eslint-plugin-expensify/no-thenable-actions-in-views.js#L24

https://github.com/Expensify/eslint-config-expensify/blob/16cef2c029311c6b3c25a83a730409d49493c766/eslint-plugin-expensify/prefer-localization.js#L42

https://github.com/Expensify/eslint-config-expensify/blob/16cef2c029311c6b3c25a83a730409d49493c766/eslint-plugin-expensify/prefer-actions-set-data.js#L18-L24

https://github.com/Expensify/eslint-config-expensify/blob/16cef2c029311c6b3c25a83a730409d49493c766/eslint-plugin-expensify/no-onyx-connect.js#L13

https://github.com/Expensify/eslint-config-expensify/blob/16cef2c029311c6b3c25a83a730409d49493c766/eslint-plugin-expensify/prefer-onyx-connect-in-libs.js#L17-L22

Two custom rules use context.getSourceCode() which was also removed (replaced by context.sourceCode):

https://github.com/Expensify/eslint-config-expensify/blob/16cef2c029311c6b3c25a83a730409d49493c766/eslint-plugin-expensify/no-call-actions-from-actions.js#L19-L25

https://github.com/Expensify/eslint-config-expensify/blob/16cef2c029311c6b3c25a83a730409d49493c766/eslint-plugin-expensify/no-multiple-api-calls.js#L8

E/App pins ESLint ^9.36.0 and uses FlatCompat from @eslint/eslintrc which needs updating for ESLint 10 compatibility:

App/eslint.config.mjs

Line 1 in 1d43910

import {FlatCompat} from '@eslint/eslintrc';

react-native-onyx pins ESLint ^9.39.2 and still carries the unused @react-native-community/eslint-config devDependency (legacy eslintrc-based config removed in ESLint 10):

https://github.com/Expensify/react-native-onyx/blob/main/package.json#L49

What changes do you think we should make in order to solve the problem?

The upgrade spans three repos and should be done in order: eslint-config-expensify first (since the others depend on it), then E/App and react-native-onyx.

Phase 1 -- eslint-config-expensify

Bump the ESLint dependency to v10 and migrate all custom rules from removed context methods to their property-based replacements.

diff --git a/package.json b/package.json
--- a/package.json
+++ b/package.json
@@ -15,7 +15,7 @@
   "dependencies": {
-    "eslint": "^9.36.0",
+    "eslint": "^10.0.0",

diff --git a/eslint-plugin-expensify/no-api-in-views.js b/eslint-plugin-expensify/no-api-in-views.js
--- a/eslint-plugin-expensify/no-api-in-views.js
+++ b/eslint-plugin-expensify/no-api-in-views.js
@@ -7,11 +7,11 @@
 function create(context) {
  return {
   Identifier(node) {
-   if (isInActionFile(context.getFilename())) {
+   if (isInActionFile(context.filename)) {
     return;
    }
 
-   if (isInTestFile(context.getFilename())) {
+   if (isInTestFile(context.filename)) {
     return;
    }

diff --git a/eslint-plugin-expensify/no-thenable-actions-in-views.js b/eslint-plugin-expensify/no-thenable-actions-in-views.js
--- a/eslint-plugin-expensify/no-thenable-actions-in-views.js
+++ b/eslint-plugin-expensify/no-thenable-actions-in-views.js
@@
   MemberExpression(node) {
-   if (!isReactViewFile(context.getFilename())) {
+   if (!isReactViewFile(context.filename)) {
     return;
    }

diff --git a/eslint-plugin-expensify/prefer-localization.js b/eslint-plugin-expensify/prefer-localization.js
--- a/eslint-plugin-expensify/prefer-localization.js
+++ b/eslint-plugin-expensify/prefer-localization.js
@@
  return {
   ObjectExpression: (node) => {
-   if (!isInActionFile(context.getFilename())) {
+   if (!isInActionFile(context.filename)) {
     return;
    }

diff --git a/eslint-plugin-expensify/prefer-actions-set-data.js b/eslint-plugin-expensify/prefer-actions-set-data.js
--- a/eslint-plugin-expensify/prefer-actions-set-data.js
+++ b/eslint-plugin-expensify/prefer-actions-set-data.js
@@
 function create(context) {
  return {
   MemberExpression(node) {
-   const filename = context.getFilename();
+   const filename = context.filename;
 
    if (!isOnyxMethodCall(node)) {
     return;
    }
 
-   if (isInTestFile(context.getFilename())) {
+   if (isInTestFile(context.filename)) {
     return;
    }
 
    const methodName = lodashGet(node, 'property.name');
-   if (!isDataSettingMethod(methodName) || isInActionFile(context.getFilename(filename))) {
+   if (!isDataSettingMethod(methodName) || isInActionFile(filename)) {
     return;
    }

diff --git a/eslint-plugin-expensify/no-onyx-connect.js b/eslint-plugin-expensify/no-onyx-connect.js
--- a/eslint-plugin-expensify/no-onyx-connect.js
+++ b/eslint-plugin-expensify/no-onyx-connect.js
@@
   MemberExpression(node) {
    if (!isOnyxMethodCall(node)) {
     return;
    }
 
-   if (isInTestFile(context.getFilename())) {
+   if (isInTestFile(context.filename)) {
     return;
    }

diff --git a/eslint-plugin-expensify/prefer-onyx-connect-in-libs.js b/eslint-plugin-expensify/prefer-onyx-connect-in-libs.js
--- a/eslint-plugin-expensify/prefer-onyx-connect-in-libs.js
+++ b/eslint-plugin-expensify/prefer-onyx-connect-in-libs.js
@@
 function create(context) {
  return {
   MemberExpression(node) {
-   const filename = context.getFilename();
+   const filename = context.filename;
 
    if (!isOnyxMethodCall(node)) {
     return;
    }
 
-   if (isInTestFile(context.getFilename())) {
+   if (isInTestFile(context.filename)) {
     return;
    }

diff --git a/eslint-plugin-expensify/no-call-actions-from-actions.js b/eslint-plugin-expensify/no-call-actions-from-actions.js
--- a/eslint-plugin-expensify/no-call-actions-from-actions.js
+++ b/eslint-plugin-expensify/no-call-actions-from-actions.js
@@
  function checkFunctionBody(node) {
-  if (!isInActionFile(context.getFilename())) {
+  if (!isInActionFile(context.filename)) {
    return;
   }
 
-  const tokens = context.getSourceCode().getTokens(node);
+  const tokens = context.sourceCode.getTokens(node);

diff --git a/eslint-plugin-expensify/no-multiple-api-calls.js b/eslint-plugin-expensify/no-multiple-api-calls.js
--- a/eslint-plugin-expensify/no-multiple-api-calls.js
+++ b/eslint-plugin-expensify/no-multiple-api-calls.js
@@
  function checkFunctionBody(node) {
-  const tokens = context.getSourceCode().getTokens(node);
+  const tokens = context.sourceCode.getTokens(node);

Phase 2 -- E/App

Bump ESLint and eslint-config-expensify to their new versions, update @eslint/eslintrc for FlatCompat compatibility with ESLint 10, and handle the three new eslint:recommended rules.

diff --git a/package.json b/package.json
--- a/package.json
+++ b/package.json
@@
   "devDependencies": {
-    "eslint": "^9.36.0",
-    "eslint-config-expensify": "2.0.105",
+    "eslint": "^10.0.0",
+    "eslint-config-expensify": "2.0.106",

ESLint 10 adds three new rules to eslint:recommended: preserve-caught-error, no-useless-assignment, and no-unassigned-vars. Since E/App already uses TypeScript-eslint's recommendedTypeChecked which provides equivalent or stricter checks, these should be configured for the codebase's needs:

diff --git a/eslint.config.mjs b/eslint.config.mjs
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@
         // ESLint core rules
         'es/no-nullish-coalescing-operators': 'off',
         'es/no-optional-chaining': 'off',
         '@typescript-eslint/no-deprecated': 'off',
         'arrow-body-style': 'off',
         'no-continue': 'off',
+
+        // ESLint 10 added these to eslint:recommended; configure as needed
+        'no-useless-assignment': 'error',
+        'no-unassigned-vars': 'error',
+        'preserve-caught-error': 'error',

Also, remove any remaining /* eslint-env */ comments from the codebase, as ESLint 10 now reports them as errors instead of silently ignoring them.

Phase 3 -- react-native-onyx

Bump ESLint and eslint-config-expensify, and remove the unused @react-native-community/eslint-config devDependency (which relies on the legacy eslintrc format that ESLint 10 no longer supports).

diff --git a/package.json b/package.json
--- a/package.json
+++ b/package.json
@@
   "devDependencies": {
-    "@react-native-community/eslint-config": "^3.2.0",
@@
-    "eslint": "^9.39.2",
-    "eslint-config-expensify": "^2.0.102",
+    "eslint": "^10.0.0",
+    "eslint-config-expensify": "^2.0.106",

The existing eslint.config.mjs in react-native-onyx already uses flat config and spreads eslint-config-expensify's array export, so no config file changes are needed beyond the dependency bumps.

All three repos already satisfy the Node.js >= v20.19.0 requirement for ESLint 10 (react-native-onyx enforces >=20.19.5 in engines, and the others use compatible CI node versions).

[PiyushChandra17]

Proposal

Please re-state the problem that we are trying to solve in this issue.

Upgrade to ESLint 10

What is the root cause of that problem?

Currently we are using outdated version of eslint ie. ^9.36.0

App/package.json

Line 303 in c359799

"eslint": "^9.36.0",

We want to upgrade it to the latest ie. ^10.0.0

What changes do you think we should make in order to solve the problem?

1. Bump the eslint: v9.36.0 to eslint: v10.0.0

npm install eslint@^10.0.0 --save-dev

• Migrate from .eslintrc.js to eslint.config.js (flat config) — required in ESLint 10

2. Run the dependency installation: npm install to install the updated version

Update related packages:

eslint-config-expensify

App/package.json

Line 305 in c359799

"eslint-config-expensify": "2.0.105",

react-native-onyx

App/package.json

Line 184 in c359799

"react-native-onyx": "3.0.41",

3. Test the changes: Run the lint checks and CI/CD workflows to ensure no issues arise from upgrade

Run Lint to surface any broken rules:

npm run lint

4. Breaking changes

• ESLint 10 drops support for Node.js < 18.18 — verify the config's engine requirements

• Flat config (eslint.config.js) is now the default in ESLint 10; update config export format

Migrate .eslintrc.* → eslint.config.js

5. Fix any rule removal errors

--rulesdir flag removed > Use plugins instead

What alternative solutions did you explore? (Optional)

n/A

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