True Myth provides safe, idiomatic null, error, and async code handling in TypeScript, with Maybe, Result, and Task types that are really nice.

README • API docs • Source • Intro blog post

True Myth provides standard, type-safe wrappers and helper functions to help you with three extremely common cases in programming:

• not having a value
• having a result where you need to deal with either success or failure
• having an asynchronous operation which may fail

You could implement all of these yourself – it's not hard! – but it's much easier to just have one extremely well-tested library you can use everywhere to solve this problem once and for all.

See the docs for setup, guides, and API docs!

• Requirements
• Compatibility
• Basic bundle size info

• TS 5.3+
• tsconfig.json:
  • moduleResolution: use "Node16" or later
  • strict: true
• package.json
  • type: "module" (or else use import() to import True Myth into a commonJS build)

For details on using a pure ES modules package in TypeScript, see the TypeScript handbook's guide.

This project follows the current draft of the Semantic Versioning for TypeScript Types specification.

• Currently supported TypeScript versions: 5.3–6.0
• Compiler support policy: simple majors
• Public API: all published, documented types not in a -private module and not marked as @internal or @private are public

Size of the ESM build without tree-shaking (yes, these are in bytes: this is a pretty small library!):

Notes:

• The unmodified size includes comments.

• Thus, running through Terser gets us a much more realistic size: about 18.1KB to parse.

• The total size across the wire of the whole library will be ~5.2KB.

• This is all tree-shakeable to a significant degree: you should only have to “pay for” the types and functions you actually use, directly or indirectly. If your production bundle does not import or use anything from true-myth/test-support, you will not pay for it, for example. However, some parts of the library do depend directly on other parts: for example, toolbelt uses exports from result and maybe, and Task makes extensive use of Result under the hood.

  In detail, here are the dependencies of each module:

  Module	Depends on
  index.js	All, but as tree-shakeable as possible
  maybe.js	unit.js, -private/utils.js
  result.js	unit.js, -private/utils.js
  standard-schema.js	task.js, result.js
  task.js	result.js, unit.js, task/delay.js, -private/utils.js
  task/delay.js	None
  test-support.js	maybe.js, result.js
  toolbelt.js	maybe.js, result.js, -private/utils.js

• This intentionally excludes the ESLint plugin contents, which should not be part of an production bundle.

The design of True Myth draws heavily on prior art; essentially nothing of this is original – perhaps excepting the choice to make Maybe.of handle null and undefined in constructing the types. In particular, however, True Myth draws particular inspiration from:

• Rust's Option and Result types and their associated methods
• Folktale's Maybe and Result implementations
• Elm's Maybe and Result types and their associated functions