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Documentation Index

Fetch the complete documentation index at: https://mintlify.com/supermacro/neverthrow/llms.txt

Use this file to discover all available pages before exploring further.

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Migration Guide

This guide helps you migrate between major versions of NeverThrow, highlighting breaking changes and how to adapt your code.

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Migrating to v8.0.0

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Breaking Change: orElse Type Arguments

Version 8.0.0 introduces a breaking change to the orElse method to allow changing Ok types, making the types match the implementation. What Changed: The orElse type argument order has changed. The ok type must now be provided before the err type. Migration Steps: 
- result.orElse<ErrType>(foo)
+ result.orElse<OkType, ErrType>(foo)
When to Update: This only applies if you explicitly provided type arguments at an orElse callsite. If the type arguments were inferred, no updates are needed during the upgrade.
Before (v7.x):
const result: Result<number, string> = err('database error')

const recovered = result.orElse<DatabaseError>((error) => {
  return ok(0)
})
After (v8.0+):
const result: Result<number, string> = err('database error')

const recovered = result.orElse<number, DatabaseError>((error) => {
  return ok(0)
})

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Migrating to v7.0.0

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Node.js Version Requirement

Version 7.0.0 declares the minimum supported Node.js version in the engines field. What Changed:
  • Minimum Node.js version is now declared as >=18
  • Minimum npm version is now declared as >=11
Note: NeverThrow does not depend on any Node.js version-specific features and should work with any version that supports ES6, including browsers, Deno, and other runtimes. The engine declaration is primarily for maintaining a consistent development environment.

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Type Inference Improvements

Version 7.0.0 includes several type inference improvements:
  • safeTry type inference: Type definitions were changed to make inferring types of safeTry more strict
  • match type inference: Enhanced type inference for the match method
  • combineWithAllErrors types: Fixed type definitions for better error handling

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Migrating from v6.x to v7.x

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safeTry Return Type Change

In v7.2.0, the return type of safeTry was changed from Promise<Result<T, E>> to ResultAsync<T, E> for better composability. What Changed: 
// v6.x and early v7.x
function safeTry(): Promise<Result<T, E>>

// v7.2.0+
function safeTry(): ResultAsync<T, E>
Why This Matters: ResultAsync is thenable and behaves like a native Promise, but provides additional methods like map, andThen, and mapErr without needing to await first. Migration: 
// Before: Need to await before chaining Result methods
const result = await safeTry(async function* () {
  // ...
})
result.map(x => x * 2)

// After: Can chain directly
safeTry(async function* () {
  // ...
}).map(x => x * 2)

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New Methods Added

v7.1.0 introduced new methods for handling side effects:
  • andTee: Handle side effects on the Ok track without affecting the error type
  • andThrough: Similar to andTee but propagates errors from the callback
  • orTee: Handle side effects on the Err track (added in v8.2.0)
These methods don’t require migration but provide cleaner patterns for logging and validation.

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Migrating from Earlier Versions

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safeTry and safeUnwrap

As of v8.1.0, safeUnwrap is deprecated. When using safeTry in v8.1.0+, you no longer need to call .safeUnwrap() on results. Before (v8.0.x and earlier): 
function myFunc(): Result<number, string> {
  return safeTry<number, string>(function*() {
    const value = yield* mayFail().safeUnwrap()
    return ok(value * 2)
  })
}
After (v8.1.0+): 
function myFunc(): ResultAsync<number, string> {
  return safeTry<number, string>(function*() {
    const value = yield* mayFail()
    return ok(value * 2)
  })
}

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Void Return Types

As of v8.2.0, ok, err, okAsync, and errAsync can accept zero arguments when returning void: 
// v8.2.0+
const result: Result<void, never> = ok()
const error: Result<never, void> = err()

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Version History Summary

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v8.2.0 (Current)

  • Added orTee method for error track side effects
  • Allow zero arguments for void returns in ok/err/okAsync/errAsync

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v8.1.0

  • safeTry no longer requires .safeUnwrap()
  • Deprecated safeUnwrap method

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v8.0.0

  • Breaking: orElse type argument order changed

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v7.2.0

  • safeTry return type changed to ResultAsync for better composability

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v7.1.0

  • Added andTee, andThrough methods
  • Fixed combineWithAllErrors types
  • Improved err() string inference

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v7.0.0

  • Declared minimum Node.js version (>=18)
  • Improved type inference for safeTry and match

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Need Help?

If you encounter issues during migration:

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