perf: optimize Object.keys() checks and optional chaining

[AbdelrahmanHafez]

Summary

• Add utils.hasOwnKeys() helper that checks for empty objects without allocating an array via Object.keys()
• Replace ~50 instances of Object.keys(obj).length pattern with hasOwnKeys(), reading the first key only instead of creating an array for all keys.
• Expand optional chaining conversions across ~78 files, including:
  • x && x.y → x?.y patterns
  • x != null && x.y → x?.y patterns
  • x && x.y && x.z → x?.y?.z deep access patterns
  • x != null ? x : default → x ?? default
  • Remove redundant null checks before Array.isArray() calls (Array.isArray already returns false for null/undefined, and performs the same)
• Cache repeated property lookups (e.g., this.$__schema.options, model.db.options)
• Optimize indexOf() calls by caching the result instead of calling twice
• Convert arguments to rest parameters in Query.prototype.slice()
• Optimize Set operations in document.overwrite() and getModelsMapForPopulate()

[Copilot]

Pull request overview

This PR implements several performance optimizations across the Mongoose codebase:

• Introduces a new utils.hasOwnKeys() helper that checks for object keys more efficiently than Object.keys().length
• Converts verbose property access chains to optional chaining syntax
• Caches repeated property lookups to avoid redundant access
• Optimizes indexOf() calls by caching results
• Converts arguments object usage to rest parameters
• Optimizes Set operations for duplicate checking

Reviewed changes

Copilot reviewed 35 out of 35 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lib/utils.js	Adds hasOwnKeys() helper function and updates isEmptyObject() to use it
lib/types/subdocument.js	Replaces Object.keys(ret).length === 0 with hasOwnKeys()
lib/types/documentArray/methods/index.js	Converts property access chains to optional chaining
lib/types/documentArray/index.js	Converts property access chains to optional chaining
lib/types/array/methods/index.js	Replaces Object.keys() length checks with hasOwnKeys()
lib/types/array/index.js	Converts property access chains to optional chaining
lib/schemaType.js	Simplifies null/undefined check to != null
lib/schema/subdocument.js	Converts to optional chaining and uses hasOwnKeys()
lib/schema/string.js	Simplifies null/undefined checks to != null
lib/schema/number.js	Simplifies null/undefined checks to != null
lib/schema/mixed.js	Replaces Object.keys() check with hasOwnKeys()
lib/schema/map.js	Replaces Object.keys() check with hasOwnKeys()
lib/schema/array.js	Converts property access chain to optional chaining
lib/schema.js	Converts to optional chaining and uses hasOwnKeys()
lib/queryHelpers.js	Converts to optional chaining
lib/query.js	Caches repeated property access, converts to rest parameters, uses hasOwnKeys(), and optional chaining
lib/plugins/trackTransaction.js	Replaces Object.keys() checks with hasOwnKeys()
lib/mongoose.js	Converts to optional chaining and uses hasOwnKeys()
lib/model.js	Converts to optional chaining and uses hasOwnKeys()
lib/helpers/update/castArrayFilters.js	Adds utils import and uses hasOwnKeys()
lib/helpers/update/applyTimestampsToUpdate.js	Adds utils import and uses hasOwnKeys()
lib/helpers/schema/getIndexes.js	Simplifies null/undefined check to != null
lib/helpers/schema/applyWriteConcern.js	Adds utils import, uses optional chaining and hasOwnKeys()
lib/helpers/schema/applyReadConcern.js	Converts to optional chaining
lib/helpers/query/castUpdate.js	Uses hasOwnKeys() for empty object checks
lib/helpers/populate/getModelsMapForPopulate.js	Optimizes duplicate checking with Set, uses optional chaining and hasOwnKeys()
lib/helpers/document/compile.js	Converts to optional chaining and uses hasOwnKeys()
lib/helpers/document/applyVirtuals.js	Adds utils import and uses hasOwnKeys()
lib/helpers/document/applyTimestamps.js	Adds utils import and uses hasOwnKeys()
lib/drivers/node-mongodb-native/connection.js	Converts to optional chaining and uses hasOwnKeys()
lib/drivers/node-mongodb-native/collection.js	Converts to optional chaining
lib/document.js	Optimizes with Set for key deduplication, caches schema options, uses hasOwnKeys()
lib/cursor/changeStream.js	Converts to optional chaining
lib/connection.js	Caches indexOf() results and uses hasOwnKeys()
lib/cast.js	Converts to optional chaining and uses hasOwnKeys()

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[Copilot]

Pull request overview

Copilot reviewed 35 out of 35 changed files in this pull request and generated no new comments.

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[vkarpov15]

Some of the changes look slower than what was originally there, most notably optional chaining and checking if Object.keys(obj).length.

[AbdelrahmanHafez]

Changing this to draft since I found a bunch of other opportunities to refactor for optional chaining and simplify code in general.

[Copilot]

Pull request overview

Copilot reviewed 83 out of 83 changed files in this pull request and generated 4 comments.

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[AbdelrahmanHafez]

@vkarpov15 This PR grew a bit larger than I initially intended, there were many places where optional chaining could improve readability and/or performance. I've reviewed it a couple of times myself, had Copilot validate it as well, and all tests and lint are passing, which should give us good confidence in these changes.

That said, if it would make things easier for you, I'm happy to split this into smaller PRs. Let me know if there's anything I can do to make the review process smoother.

[vkarpov15]

This PR's great, no need for separate PRs. Thanks 👍