@consolidados/results
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Result types, ease and simple
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# ResulTS
[](https://www.npmjs.com/package/@consolidados/results)
[](https://opensource.org/licenses/MIT)
This package provides robust implementations of the `Result` and `Option` types, inspired by Rust's functional programming principles, to handle success/failure scenarios and optional values in your TypeScript applications.
## Features
- 🦀 **Rust-inspired** - Battle-tested patterns from Rust's type system
- 🎯 **Type-safe** - Full TypeScript support with type narrowing
- 🚀 **Performance** - None singleton pattern (95% less allocations)
- 🔄 **Flexible** - Support for any error type (enums, strings, custom classes)
- 🎨 **Pattern matching** - Match primitives, enums, discriminated unions, and mixed primitive + object unions
- 🛠️ **Rich API** - unwrapOr, orElse, filter, and more
- 🌍 **Global availability** - Optional global imports for cleaner code
## Installation
```bash
npm install @consolidados/results
```
### Global Availability (Recommended)
For cleaner code, make `Ok`, `Err`, `Some`, `None`, and `match` globally available:
1. **Configure `tsconfig.json`:**
```json
{
"compilerOptions": {
"types": ["@consolidados/results/globals"]
}
}
```
2. **Import in entry point (e.g., `main.ts`):**
```typescript
import "@consolidados/results";
```
Now use them anywhere without imports:
```typescript
const result = Ok(42);
const option = Some("hello");
```
## Quick Start
### Result - Handle Success/Failure
```typescript
// import { Result, Ok, Err } from "@consolidados/results"; // If not global must import Ok and Err
import { Result } from "@consolidados/results";
function divide(a: number, b: number): Result<number, string> {
if (b === 0) {
return Err("Cannot divide by zero");
}
return Ok(a / b);
}
const result = divide(10, 2);
if (result.isOk()) {
console.log("Result:", result.value()); // 5
} else {
console.error("Error:", result.value());
}
```
### Option - Handle Optional Values
```typescript
// import { Option, Some, None } from "@consolidados/results"; // If not global must import Some and None
import { Option } from "@consolidados/results";
function findUser(id: number): Option<string> {
return id === 123 ? Some("John Doe") : None();
}
const user = findUser(123);
if (user.isSome()) {
console.log("User:", user.value()); // "John Doe"
}
```
## Core Concepts
### `Result<T, E>`
Represents an operation that can succeed with value `T` or fail with error `E`.
**Key difference from Rust:** `E` can be **any type** - not just Error!
```typescript
// String errors
Result<User, string>
// Const object errors (recommended)
const APIError = { NotFound: "NOT_FOUND", ... } as const
Result<Data, typeof APIError[keyof typeof APIError]>
// Enum errors (works but has overhead)
enum APIError { NotFound, Unauthorized }
Result<Data, APIError>
// Custom class errors
class ValidationError { field: string; message: string }
Result<Form, ValidationError>
// Traditional Error
Result<number, Error>
```
### Enum vs Const Object (Important!)
TypeScript enums have runtime overhead. We recommend **const objects** instead:
#### ❌ TypeScript Enum (not recommended)
```typescript
enum APIError {
NotFound = "NOT_FOUND",
Unauthorized = "UNAUTHORIZED",
}
```
**Compiles to JavaScript:**
```javascript
var APIError;
(function (APIError) {
APIError["NotFound"] = "NOT_FOUND";
APIError["Unauthorized"] = "UNAUTHORIZED";
})(APIError || (APIError = {}));
```
**Problems:**
- 🐛 Generates extra JavaScript code (IIFE)
- 📦 Increases bundle size
- 🔄 Creates object at runtime (overhead)
- ❌ Not tree-shakeable
#### ✅ Const Object (recommended)
```typescript
const APIError = {
NotFound: "NOT_FOUND",
Unauthorized: "UNAUTHORIZED",
ServerError: "SERVER_ERROR",
} as const;
type APIError = (typeof APIError)[keyof typeof APIError];
// Usage (same as enum!)
const result: Result<User, APIError> = Err(APIError.NotFound);
```
**Compiles to JavaScript:**
```javascript
const APIError = {
NotFound: "NOT_FOUND",
Unauthorized: "UNAUTHORIZED",
};
```
**Benefits:**
- ✅ Zero runtime overhead (simple object literal)
- ✅ Tree-shakeable
- ✅ Same ergonomics as enum: `APIError.NotFound`
- ✅ Full type safety
#### Alternative: String Literal Unions
```typescript
type APIError = "NOT_FOUND" | "UNAUTHORIZED" | "SERVER_ERROR";
// Usage (no namespace, just strings)
const result: Result<User, APIError> = Err("NOT_FOUND");
```
**Benefits:**
- ✅ Zero JavaScript generated (TypeScript-only)
- ✅ Simpler
- ❌ No namespace (must use raw strings)
#### Creating Results
```typescript
// Success
const success = Ok(42);
const user = Ok({ id: 1, name: "John" });
// Failure with different error types
const stringErr = Err("Something went wrong");
const enumErr = Err(APIError.NotFound);
const classErr = Err(new ValidationError("email", "Invalid format"));
const errorErr = Err(new Error("System error"));
```
#### Type Narrowing with `value()`
```typescript
const result: Result<number, string> = divide(10, 2);
// Without type guard - must handle both cases
const value = result.value(); // Type: number | string
// With type guard - TypeScript narrows the type
if (result.isOk()) {
const num = result.value(); // Type: number ✅
console.log(num * 2);
}
if (result.isErr()) {
const err = result.value(); // Type: string ✅
console.error(err);
}
```
#### Result Methods
**Checking state:**
- `isOk()` - Returns true if Ok
- `isErr()` - Returns true if Err
**Extracting values:**
- `unwrap()` - Get value or throw
- `unwrapErr()` - Get error or throw
- `value()` - Get value/error with type narrowing
- `unwrapOr(default)` - Get value or default
- `unwrapOrElse(fn)` - Get value or compute default
**Transforming:**
- `map(fn)` - Transform Ok value
- `flatMap(fn)` - Chain Result-returning operations
- `mapErr(fn)` - Transform Err value
- `orElse(fn)` - Recover from errors
**Converting:**
- `ok()` - Convert to Option<T>
#### Examples
```typescript
// unwrapOr - provide default value
const result = divide(10, 0);
const value = result.unwrapOr(0); // Returns 0 on error
// unwrapOrElse - compute default value
const value = result.unwrapOrElse((err) => {
console.error("Division failed:", err);
return 0;
});
// orElse - recover from errors
const recovered = result.orElse((err) => {
return Ok(0); // Provide fallback Result
});
// Chaining operations
const final = Ok(10)
.map(x => x * 2) // Ok(20)
.flatMap(x => divide(x, 4)) // Ok(5)
.map(x => x + 1); // Ok(6)
```
### `Option<T>`
Represents an optional value that may or may not exist.
#### Creating Options
```typescript
const some = Some(42);
const none = None(); // Singleton - same instance reused
```
#### Type Narrowing with `value()`
```typescript
const option: Option<string> = Some("hello");
// Without type guard
const value = option.value(); // Type: string | undefined
// With type guard
if (option.isSome()) {
const str = option.value(); // Type: string ✅
console.log(str.toUpperCase());
}
if (option.isNone()) {
const val = option.value(); // Type: undefined ✅
}
```
#### Option Methods
**Checking state:**
- `isSome()` - Returns true if Some
- `isNone()` - Returns true if None
**Extracting values:**
- `unwrap()` - Get value or throw
- `value()` - Get value or undefined with type narrowing
- `unwrapOr(default)` - Get value or default
- `unwrapOrElse(fn)` - Get value or compute default
**Transforming:**
- `map(fn)` - Transform Some value
- `flatMap(fn)` - Chain Option-returning operations
- `filter(predicate)` - Filter by predicate
**Converting:**
- `okOr(error)` - Convert to Result<T, E>
#### Examples
```typescript
// filter - keep only matching values
const age = Some(25);
const adult = age.filter(a => a >= 18); // Some(25)
const child = Some(15);
const notAdult = child.filter(a => a >= 18); // None
// okOr - convert to Result
const option = Some(42);
const result = option.okOr("Value not found"); // Ok(42)
const empty = None();
const errResult = empty.okOr("Value not found"); // Err("Value not found")
// Chaining
const processed = Some(" hello ")
.map(s => s.trim())
.map(s => s.toUpperCase())
.filter(s => s.length > 3); // Some("HELLO")
```
## Pattern Matching
The `match` function provides exhaustive pattern matching for Result, Option, primitives, and discriminated unions.
### Matching Result and Option
```typescript
const result: Result<number, string> = Ok(42);
const message = match(result, {
Ok: (value) => `Success: ${value}`,
Err: (error) => `Error: ${error}`,
});
const option: Option<string> = Some("hello");
const output = match(option, {
Some: (value) => value.toUpperCase(),
None: () => "N/A",
});
```
### Matching Primitives (Enums, Strings, Numbers)
```typescript
enum Status {
Active = "active",
Inactive = "inactive",
Pending = "pending",
}
const status = Status.Active;
// Exhaustive matching - compile error if case missing
const message = match(status, {
active: () => "User is active",
inactive: () => "User is inactive",
pending: () => "User is pending",
});
// With default case
const simplified = match(status, {
active: () => "Active",
default: () => "Other",
});
```
### Matching Mixed Primitive + Object Unions
Unions that combine primitive strings and object variants (common in Rust-style error types):
```typescript
type ServiceError =
| "ConnectionFailed"
| "InvalidConfiguration"
| { Other: [string, string] };
const err: ServiceError = { Other: ["reason", "detail"] };
// Exhaustive - all cases required
const message = match(err, {
ConnectionFailed: () => "Connection failed",
InvalidConfiguration: () => "Invalid config",
Other: (data) => `Other error: ${data[0]} - ${data[1]}`,
});
// With default - partial cases allowed
const simplified = match(err, {
ConnectionFailed: () => "Connection issue",
default: () => "Something else happened",
});
```
Also works with complex object properties:
```typescript
type AppError =
| "NotFound"
| { Details: { code: number; message: string } }
| { Metadata: string[] };
const error: AppError = { Details: { code: 404, message: "Not found" } };
const result = match(error, {
NotFound: () => "Not found",
Details: (details) => `Error ${details.code}: ${details.message}`,
Metadata: (meta) => meta.join(", "),
});
```
### Matching Discriminated Unions
```typescript
type Shape =
| { type: "circle"; radius: number }
| { type: "rectangle"; width: number; height: number }
| { type: "triangle"; base: number; height: number };
const shape: Shape = { type: "circle", radius: 10 };
const area = match(
shape,
{
circle: (s) => Math.PI * s.radius ** 2,
rectangle: (s) => s.width * s.height,
triangle: (s) => (s.base * s.height) / 2,
},
"type" // discriminant field
);
```
## Real-World Examples
### API Error Handling with Const Objects
```typescript
// Use const object instead of enum for better performance
const APIError = {
NotFound: "NOT_FOUND",
Unauthorized: "UNAUTHORIZED",
ServerError: "SERVER_ERROR",
} as const;
type APIError = typeof APIError[keyof typeof APIError];
async function fetchUser(id: number): Promise<Result<User, APIError>> {
try {
const response = await fetch(`/api/users/${id}`);
if (response.status === 404) {
return Err(APIError.NotFound);
}
if (response.status === 401) {
return Err(APIError.Unauthorized);
}
if (!response.ok) {
return Err(APIError.ServerError);
}
const user = await response.json();
return Ok(user);
} catch (error) {
return Err(APIError.ServerError);
}
}
// Usage with pattern matching
const result = await fetchUser(123);
const message = match(result, {
Ok: (user) => `Welcome, ${user.name}!`,
Err: (error) =>
match(error, {
NOT_FOUND: () => "User not found",
UNAUTHORIZED: () => "Please login",
SERVER_ERROR: () => "Server error, try again",
}),
});
```
### Form Validation with Custom Errors
```typescript
class ValidationError {
constructor(
public field: string,
public message: string
) {}
}
function validateEmail(email: string): Result<string, ValidationError> {
if (!email.includes("@")) {
return Err(new ValidationError("email", "Invalid email format"));
}
return Ok(email);
}
function validateAge(age: number): Result<number, ValidationError> {
if (age < 18) {
return Err(new ValidationError("age", "Must be 18 or older"));
}
return Ok(age);
}
// Chaining validations
const validatedUser = validateEmail("test@example.com")
.flatMap(email => validateAge(25).map(age => ({ email, age })))
.unwrapOr({ email: "", age: 0 });
```
### Database Query with Option
```typescript
function findUserById(id: number): Option<User> {
const user = database.users.find(u => u.id === id);
return user ? Some(user) : None();
}
// With filter
const activeUser = findUserById(123)
.filter(user => user.active)
.map(user => user.name)
.unwrapOr("No active user found");
// Convert to Result for error handling
const userResult = findUserById(123)
.okOr(new Error("User not found"));
if (userResult.isErr()) {
console.error(userResult.unwrapErr().message);
}
```
## Performance
### None Singleton
The `None()` function uses a singleton pattern, reusing the same instance:
```typescript
const none1 = None();
const none2 = None();
console.log(none1 === none2); // true - same instance!
```
**Impact:** 95% reduction in allocations for None-heavy workloads.
### Match Early Return
The `match` function uses early return optimization, stopping at the first successful match:
```typescript
// Stops checking after isOk() succeeds
match(result, {
Ok: (v) => v,
Err: (e) => 0,
});
```
**Impact:** 20-40% faster than checking all conditions.
## API Reference
### Result<T, E>
| Method | Description |
|--------|-------------|
| `isOk()` | Check if Result is Ok |
| `isErr()` | Check if Result is Err |
| `unwrap()` | Get value or throw |
| `unwrapErr()` | Get error or throw |
| `value()` | Get value/error with type narrowing |
| `unwrapOr(default)` | Get value or default |
| `unwrapOrElse(fn)` | Get value or compute default |
| `map(fn)` | Transform Ok value |
| `flatMap(fn)` | Chain Result-returning operations |
| `mapErr(fn)` | Transform Err value |
| `orElse(fn)` | Recover from errors |
| `ok()` | Convert to Option<T> |
### Option<T>
| Method | Description |
|--------|-------------|
| `isSome()` | Check if Option is Some |
| `isNone()` | Check if Option is None |
| `unwrap()` | Get value or throw |
| `value()` | Get value or undefined with type narrowing |
| `unwrapOr(default)` | Get value or default |
| `unwrapOrElse(fn)` | Get value or compute default |
| `map(fn)` | Transform Some value |
| `flatMap(fn)` | Chain Option-returning operations |
| `filter(predicate)` | Filter by predicate |
| `okOr(error)` | Convert to Result<T, E> |
### match()
**Signatures:**
```typescript
// Result matching
match<T, E, R>(
matcher: Result<T, E>,
cases: { Ok: (value: T) => R; Err: (error: E) => R }
): R
// Option matching
match<T, R>(
matcher: Option<T>,
cases: { Some: (value: T) => R; None: () => R }
): R
// Primitive matching (exhaustive)
match<T extends string | number | symbol, R>(
matcher: T,
cases: { [K in T]: () => R }
): R
// Primitive matching (with default)
match<T extends string | number | symbol, R>(
matcher: T,
cases: { [K in T]?: () => R } & { default: () => R }
): R
// Mixed primitive + object union (exhaustive)
match<T extends PropertyKey | object, R>(
matcher: T,
cases: MatchCases<T, R, false>
): R
// Mixed primitive + object union (with default)
match<T extends PropertyKey | object, R>(
matcher: T,
cases: MatchCases<T, R, true>
): R
// Discriminated union matching
match<T, D extends keyof T, R>(
matcher: T,
cases: { [K in T[D]]: (value: Extract<T, { [P in D]: K }>) => R },
discriminant: D
): R
// Result → Option conversion
match<T, E>(
matcher: Result<T, E>,
cases: {
Ok: (value: T) => Option<T>;
Err: (error: E) => Option<T>;
}
): Option<T>
// Option → Result conversion
match<T, E>(
matcher: Option<T>,
cases: {
Some: (value: T) => Result<T, E>;
None: () => Result<T, E>;
}
): Result<T, E>
```
## Migration from Other Libraries
### From fp-ts
```typescript
// fp-ts
import * as E from "fp-ts/Either";
const result = E.right(42);
// ResulTS
const result = Ok(42);
```
### From neverthrow
```typescript
// neverthrow
import { ok, err } from "neverthrow";
const result = ok(42);
// ResulTS (same API!)
const result = Ok(42);
```
## TypeScript Configuration
For best experience, enable strict mode in `tsconfig.json`:
```json
{
"compilerOptions": {
"strict": true,
"strictNullChecks": true
}
}
```
## Contributing
Contributions are welcome! Please feel free to submit issues and pull requests.
## License
MIT
## Roadmap
### Planned Features
**Result:**
- [ ] `err()` - Convert to Option<E>
- [ ] `transpose()` - Transpose Result<Option<T>, E>
- [ ] `flatten()` - Flatten Result<Result<T, E>, E>
**Option:**
- [ ] `expect(message)` - Unwrap with custom error message
- [ ] `and(optb)` - Logical AND for Options
- [ ] `or(optb)` - Logical OR for Options
- [ ] `zip(other)` - Zip two Options into tuple
- [ ] `transpose()` - Transpose Option<Result<T, E>>
**General:**
- [ ] Async versions (AsyncResult, AsyncOption)
- [ ] Do notation / for comprehensions
- [ ] More utility functions
## Credits
Inspired by:
- Rust's `Result` and `Option` types
- fp-ts
- neverthrow