Background

PR #10782 added the ES2023 context argument to the parseReviver type:

parseReviver?: (this: any, key: string, value: any, context?: { source: string }) => any;

This is correct as far as it goes, but is slightly looser than the spec.

The Gap

Per the TC39 proposal-json-parse-with-source, context.source is only set when the reviver is invoked on a primitive value (string, number, boolean, null). When the reviver is invoked on an object or array, source is absent from the context object.

The current typing says "if context is provided, source is always a string." That's true for primitives but not for object/array reviver invocations. A user can legally write:

parseReviver: (key, value, context) => {
  if (typeof value === 'object') {
    return context.source.length; // types say string, runtime undefined -> crash
  }
}

Fix

Mark source as optional:

parseReviver?: (this: any, key: string, value: any, context?: { source?: string }) => any;

Applied to both index.d.ts and index.d.cts.

Fixes #10817

Summary by cubic

Make parseReviver context source optional in AxiosRequestConfig to match ES2023 JSON.parse with source. Corrects typing that implied source was always present; no runtime changes.

Description

• Summary of changes
  • Updated parseReviver type to context?: { source?: string } in index.d.ts and index.d.cts.
  • Merged latest v1.x with no additional functional changes.
• Reasoning
  • ES2023 sets context.source only for primitive values; it’s absent for objects/arrays.
• Additional context
  • TypeScript users should guard context?.source before use.

Docs

• Update /docs/ to note context.source is optional and present only for primitives, with a short guarded example.

Testing

• No runtime tests changed.
• Recommend a small type test to ensure context.source is optional and narrows with guards.

Semantic version impact

Patch: typings corrected to match the spec; no runtime API changes.

^{Written for commit f9372e5. Summary will update on new commits.}