[dohwi]

Summary

Closes #1707. Enable error-aware retry intervals by passing the error object to the delay callback, consistent with how shouldRetry already receives it.

Changes

• delay callback now receives (attempts: number, error: unknown) — error is passed as the second argument alongside the attempt number
• delay?: number | ((attempts: number, error: unknown) => number) type updated in both the RetryOptions interface and implementation
• Added a test verifying delay receives the correct error on retry
• Updated documentation in all 4 languages (en, ko, ja, zh_hans) with error-aware delay examples

Test results

✓ src/function/retry.spec.ts (10 tests) 175ms
  ✓ should pass error to delay function
  ✓ should retry with a dynamic delay function (backward compat)
  ... 8 more all passing

Full suite: 560 test files, 4482 tests passed, 0 failures.

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Project	Deployment	Actions	Updated (UTC)
es-toolkit	Ready	Preview	Aug 16, 2026 7:19am

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds error-aware retry delays by extending the delay callback signature to receive the thrown error, with updated docs and tests to reflect the new behavior.

Changes:

• Extend RetryOptions.delay function type to (attempts, error) => number and pass the error when computing delay.
• Add a unit test verifying the error is provided to the delay callback.
• Update English + localized docs with an error-based delay example and updated type signatures.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/function/retry.ts	Updates delay callback type and passes the caught error into delay computation; updates JSDoc.
src/function/retry.spec.ts	Adds test coverage for passing the error to delay.
docs/reference/function/retry.md	Documents error-aware delay usage and updates delay option signature.
docs/zh_hans/reference/function/retry.md	Same as above (Simplified Chinese).
docs/ko/reference/function/retry.md	Same as above (Korean).
docs/ja/reference/function/retry.md	Same as above (Japanese).

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[dohwi]

Thanks @copilot-pull-request-reviewer for the review.

• Comment on error variable (line 149): The error variable is declared at line 131 in the outer function scope (let error;) and assigned in the catch block (error = err;). By line 149, error is always populated — the catch parameter err and the outer variable error are distinct. This is a false positive.

• Comments on attempt vs attempts (lines 10, 91): Good catch — fixed in the latest commit.

• ResponseError not defined in docs example: Fixed — replaced with a self-contained type narrowing using (error as { status?: number }).