Getting Started
Install and use "@deessejs/fp" in your project
Installation
bash npm install @deessejs/fp bash pnpm add @deessejs/fp bash yarn add @deessejs/fp @deessejs/fp requires TypeScript 5.0 or later.
Peer dependency
@deessejs/fp uses structured errors from @deessejs/errors for advanced error handling:
npm install @deessejs/errorsThis is optional — the library works without it.
Your first Result
import { ok, err } from '@deessejs/fp';
// A function that can fail
function divide(a: number, b: number) {
if (b === 0) {
return err('Division by zero');
}
return ok(a / b);
}
const result = divide(10, 2);
// Check the result
if (result.isOk()) {
console.log(result.value); // 5
} else {
console.error(result.error); // 'Division by zero'
}Transform with map
import { ok, err } from '@deessejs/fp';
const result = ok(5)
.map((n) => n * 2) // Ok(10)
.map((n) => n + 1); // Ok(11)
result.getOrElse(0); // 11Chain operations with flatMap
import { ok, err } from '@deessejs/fp';
function findUser(id: string) {
return id === '1' ? ok({ id: '1', name: 'Alice' }) : err('Not found');
}
ok('1')
.flatMap((id) => findUser(id))
.map((user) => user.name) // Ok('Alice')
.getOrElse('Unknown'); // 'Alice'Handle optional values with Maybe
import { some, none, maybe } from '@deessejs/fp';
// Create from a nullable value
maybe(null); // None
maybe(undefined); // None
maybe('hello'); // Some('hello')
// Safe property access
const user = { name: 'Alice', address: { city: 'Paris' } };
some(user)
.flatMap((u) => maybe(u.address))
.map((addr) => addr.city) // Some('Paris')
.getOrElse('Unknown'); // 'Paris'Pattern matching
import { ok, err, some, none } from '@deessejs/fp';
// Result
const result = ok(42);
result.match({
ok: (value) => `Got ${value}`,
err: (error) => `Error: ${error}`,
}); // 'Got 42'
// Maybe
const maybeName = some('Alice');
maybeName.match({
some: (name) => `Hello, ${name}`,
none: () => 'Hello, stranger',
}); // 'Hello, Alice'