True Myth

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

Overview

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!

Contents

Requirements

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.

Compatibility

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

Currently supported TypeScript versions: 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, and 5.9
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

Basic bundle size info

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

file	size (B)	terser¹ (B)	terser and brotli² (B)
-private/utils.js	888	321	166
index.js	644	352	122
maybe.js	18872	3637	908
result.js	15274	3927	972
standard-schema.js	5975	762	317
task/delay.js	3901	649	259
task.js	54755	7448	2025
test-support.js	473	142	89
toolbelt.js	3739	890	277
unit.js	656	58	57
total³	105177	18186	5192

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`

Inspiration

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

Using terser 5.37.0 with --compress --mangle --mangle-props. ↩
Generated by running gzip -kq11 on the result of the terser invocation. ↩
This is just the sum of the previous lines. Real-world bundle size is a function of what you actually use, how your bundler handles tree-shaking, and how the results of bundling compresses. Notice that sufficiently small files can end up larger after compression; this stops being an issue once part of a bundle. ↩