refactor(commons): Replace the _ utilities with standalone functions (v6) - #3724

Summary

feathers/commons exported a lodash-like _ object. Feathers itself only uses _.pick (once, in the fetch client) and stripSlashes. Most of the other helpers have native replacements. Even the v5 ecosystem (adapter-commons, knex, mongodb, schema, rest-client, oauth) only used _.omit, _.pick and _.isObject. The commons are now a folder of standalone, typed functions:

 packages/feathers/src/
-├── commons.ts          # _ { each, some, every, keys, values, isMatch, isEmpty, isObject,
-│                       #     isObjectOrArray, extend, omit, pick, merge }, stripSlashes,
-│                       #     isPromise, createSymbol, export * from './debug.js'
-├── commons.test.ts
+└── commons/
+    ├── index.ts
+    ├── object.ts       # isObject, pick, omit (typed with generics)
+    ├── object.test.ts
+    ├── path.ts         # stripSlashes
+    └── path.test.ts

• feathers/commons now exports exactly isObject, pick, omit and stripSlashes, in both the ESM and CJS builds.
• _ is removed, together with isPromise, createSymbol and the debug re-export. The debug functions (createDebug, setDebug) are still exported from feathers.
• SERVICE now uses Symbol.for('@feathersjs/service') directly instead of createSymbol(). The value is the same.
• The typed pick found that toError in the fetch client picks address, port and config from a value whose type has none of them, so those fields are now declared on its parameter type. The ECONNREFUSED branch there looks like a leftover from the axios/request clients, since fetch rejects with a TypeError that has a cause. That is left for a follow-up.
• Dropping merge also removes the code path that needed the prototype pollution fix in fix(feathers): skip prototype-polluting keys in _.merge #3689.

Since there is no _ object any more, bundlers can tree-shake unused helpers.

No related issues, and no dependencies on other PRs.

Evidence

import * as c from 'feathers/commons'   ->  isObject, omit, pick, stripSlashes
require('feathers/commons')             ->  isObject, omit, pick, stripSlashes
SERVICE === Symbol.for('@feathersjs/service')  ->  true

• Before: Test Files 30 passed, Tests 497 passed | 1 skipped
  After: Test Files 31 passed, Tests 484 passed | 1 skipped. The 17 tests for _, isPromise and createSymbol are removed, and 4 tests for stripSlashes, isObject, pick and omit are added. npm test passes on Node.js 24 and 26, and CI is green on 20.x and 24.x.

Merge Danger

Door: two-way

Blast Radius: small

• This is a breaking change for anyone using _, isPromise or createSymbol from feathers/commons in the v6 prereleases. Replacements for the migration guide:
  • _.keys / _.values / _.extend → Object.keys / Object.values / Object.assign
  • _.each / _.some / _.every → Object.entries() / Object.values().some() / .every()
  • _.isEmpty(x) → Object.keys(x).length === 0
  • _.merge → structuredClone or a custom deep merge
  • isPromise(x) → typeof x?.then === 'function'
  • createSymbol(name) → Symbol.for(name)
• There are small conflicts with chore: Migrate to ESLint 10 flat config with @feathers-community/eslint-config (v6) #3721, which edits commons.test.ts and client/fetch.ts, and chore: Publish feathers as ESM only (v6) #3723, which edits the ./commons export. Whichever PR is merged second needs a rebase.

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