@rslike/std

Rust-Like Standard Library

Make Javascript without undefined behavior. Forgot about try/catch/finally which breakes your code!

Reasons to install @rsLike/std?

1. Less undefined behavior, when using Option and Result.
2. Well tested. 100% test coverage
3. JSDoc with examples.
4. Typescript ready - d.ts types are generated with tsc.
5. first-class CJS and ESM support.
6. Zero dependencies.
7. 2kB for min+gzip and 7.6kB for minified. See in bundlefobia.
8. Deno?

Installation

NPM:

npm i @rslike/std

YARN/PNPM/Bun:

yarn add @rslike/std
pnpm add @rslike/std
bun add @rslike/std

Wiki

Avaliable by link: https://github.com/vitalics/rslike/wiki

Adding global functions and classes

1. Install package
2. In your entry file write next:

// your main file

// add global types in globalThis Some,None,Option, Result,Ok,Err functions
import "@rslike/std/globals";

// rest your file

Related packages

• cmp
• dbg

API

Match

Matches the Option or Result and calls callback functions.

1 callback function will be executed for Ok or Some result.

2 callback function will be executed for Err or None result.

If incoming arguments is not Option or Result or callback functions is not a functions then it throws an UndefinedBehavior error.

If your result have type Result<Option<T>, E>. You need to call match function only once

const resFromBackend = Bind(async (...args) => return (await fetch(...args)).json())

const json = match(await resFromBackend('https://json-placeholder.typicode.com/posts/1'), (res) => {
    console.log('JSON is:', unwrapped)
}, (e) => {
  if(e){
    console.log('Error:', e)
  }
  else {
    console.log('JSON is None(null or undefined)')
  }
})

console.log(json); // YOUR JSON from Backend

Bind

Function decorator. Combines Result and Option modules. Make the function safe to execute.

Wraps function and return new function with binded context.

Result of this function will be mapped into Result<Option<T>,E>.

Function result will be mapped into Ok(Some(result)).

undefined function result will mapped into Ok(None()).

const fn = (a: number) => a + 2;
const newFn = Bind(fn);

const res = newFn(1);
res.unwrap().unwrap(); // 3
newFn(10).unwrap().unwrap(); // 12

const thrower = () => {
  throw new Error("shit happens :)");
};
const func = Bind(thrower);
func().isErr(); // true
const err = func().unwrapErr();
console.log(err); // {message: 'shit happens :)'}
err instanceof Error; // true

// async example
const asyncFn = () => Promise.resolve(123);
const fn = Bind(asyncFn);

const r = await fn();

r.isOk(); // true
r.unwrap(); // 123

UndefinedBehaviorError

Error that occurs when an operation is not supported, or when result is unpredictable.

Option

Type Option represents an optional value: every Option is either Some and contains a value, or None, and does not. Option have a number of uses:

• Initial values
• Return values for functions that are not defined over their entire input range (partial functions)
• Return value for otherwise reporting simple errors, where None is returned on error
• Optional struct fields
• Optional function arguments
• Nullish(null or undefined) value.
• Swapping things out of difficult situations
• Options are commonly paired with pattern matching to query the presence of a value and take action, always accounting for the None case.

Functions

Some(T)

represents Some value.

const a = Some(123);

const b = Some(null); // None()

NOTE: Some(undefined) and Some(null) automatically converted to None().

Some function is also instance of Option class and Some function.

Some(4) instanceof Option; // true
Some(4) instanceof Some; // true,

Some(4) instanceof None; // false

None

Represents nullish(null or undefiend) value

const a = None(); // Option<undefined>
const a = None(null); // Option<null>

None function is also instance of Optionclass and None function.

const a = Some(123);
const b = None();

a instanceof Option; // true
b instanceof Option; // true

a instanceof Some; // true
a instanceof None; // false

b instanceof Some; // false
b instanceof None; // true

constructor(executor)

• executor - function that receives a some and none functions as arguments.

  • some(value) - function that receives a value and returns Option instance in Some status. NOTE: some(undefined) and some(null) automatically converted to None().

  • none(reason) - function that returns Option instance in None status.

NOTE: throws UndefinedBehaviorError if value returns Promise, or executor function is async.

// return/throw results
const a = new Option(() => 4); // Option<number>
a.isSome(); // true

const b = new Option(() => {
  throw new Error("error");
});
b.isNone(); // true

// control flow functions
const c = new Option((some, none) => {
  return Math.random() > 0.5 ? some(42) : none();
}); // Option<number>

// automatic conversion
const d = new Option((some) => {
  some(null);
});
d.isSome(); // false
d.isNone(); // true

The next code will throws UndefinedBehaviorError

new Option((some, none) => {
  // throws since return Promise
  return Promise.resolve(Math.random() > 0.5 ? some(42) : none());
}); // throws UndefinedBehaviorError

new Option(async (some, none) => {
  // throws since async function
  return some(5);
}); // throws UndefinedBehaviorError

Static fields/methods

Status

Returns object with possible statuses

Option.Status = {
  Some: "Some",
  None: "None",
};

fromPromise/fromAsync

Converts a Promise into an Option.

We recommend using Bind function to handle functions since it allows to handle both regular and async functions and transform it into Result<Option<T>, E>.

await Option.fromPromise(Promise.resolve(42)); // Option<number>
await Option.fromPromise<Error>(Promise.reject(new Error("error"))); // Option<Error>
async function doAction() {
  return 42;
}

await Option.fromPromise(doAction()); // Option<number>
// but best solution is to use Bind function
const doActionSafe = Bind(doAction);

await doActionSafe(); // Result<Option<number>, unknown>

withResolvers

Returns an object with option and some, none functions. Similar to Promise.withResolvers

const { option, some, none } = Option.withResolvers();

console.log(some(2)); // (value: number) => Option<number>
console.log(option.unwrap()); // 2

none(); // doing noting. result is already set to 2

is(value)

Returns true if the value instance of Option.

None

Similar to None function.

Some

Similar to Some function.

Instance fields/methods

expect

Returns the contained Some value, consuming the self value.

const x = Some("value");
x.expect("fruits are healthy") === "value"; // true

const y: Option<string> = None();
y.expect("fruits are healthy"); // throws with `fruits are healthy`

unwrap

Returns the contained Some value, consuming the self value.

Because this function may throws, its use is generally discouraged. Instead, prefer to use pattern matching and handle the None case explicitly, or call unwrapOr, unwrapOrElse, or unwrapOrDefault.

Throws an error when value is None

const x = Some("air");
x.unwrap() === "air";

const x: Option<string> = None();
x.unwrap(); // fails

unwrapOr

Returns the contained Some value or a provided default.

const x = Some("air");
x.unwrapOr("another") === "air";

const x: Option<string> = None();
x.unwrapOr("another") === "another";

unwrapOrElse

Returns the contained Some value or computes it from a closure.

const k = 10;
Some(4).unwrapOrElse(() => 2 * k) === 4;
None().unwrapOrElse(() => 2 * k) === 20;

map

Maps an Option<T> to Option<U> by applying a function to a contained value (if Some) or returns None (if None).

const maybeSomeString = Some("Hello, World!");
const maybeSomeLen = maybeSomeString.map(s => s.length);
maybeSomeLen === Some(13));

const x: Option<string> = None();
x.map(s => s.length) === None();

mapOr

Returns the provided default result (if none), or applies a function to the contained value (if any).

Arguments passed to mapOr are eagerly evaluated; if you are passing the result of a function call, it is recommended to use mapOrElse, which is lazily evaluated.

const x = Some("foo");
x.mapOr(42, (v) => v.length) === 3;

const x: Option<string> = None();
x.mapOr(42, (v) => v.len()) === 42;

mapOrElse

Computes a default function result (if none), or applies a different function to the contained value (if any).

const k = 21;

const x = Some("foo");
x.mapOrElse(
  () => 2 * k,
  (v) => v.length
) === 3;

const x: Option<string> = None();
x.mapOrElse(
  () => 2 * k,
  (v) => v.length
) === 42;

okOr

Transforms the Option<T> into a Result<T, E>, mapping Some(v) to Ok(v) and None to Err(err).

Arguments passed to okOr are eagerly evaluated; if you are passing the result of a function call, it is recommended to use okOrElse, which is lazily evaluated.

const x = Some("foo");
String(x.okOr(0)) === String(Ok("foo"));

const y: Option<string> = None();
y.okOr(0) === Err(0);

okOrElse

Transforms the Option<T> into a Result<T, E>, mapping Some(v) to Ok(v) and None to Err(err()).

const x = Some("foo");
console.assert(x.okOrElse(() => 0) === Ok("foo"));

let y: Option<string> = None();
console.assert(y.okOrElse(() => 0) === Err(0));

and

Returns None if the option is None, otherwise returns optb.

Arguments passed to and are eagerly evaluated; if you are passing the result of a function call, it is recommended to use andThen, which is lazily evaluated.

const x = Some(2);
const y: Option<string> = None();
console.assert(x.and(y) === None());
// another example
let x: Option<number> = None();
let y = Some("foo");
console.assert(x.and(y) === None());
// another example
let x = Some(2);
let y = Some("foo");
console.assert(x.and(y) === Some("foo"));
// another example
let x: Option<number> = None();
let y: Option<string> = None();
console.assert(x.and(y) === None());

andThen

Returns None if the option is None, otherwise calls f with the wrapped value and returns the result.

Some languages call this operation flatmap.

function toString(x: number): Option<string> {
 return Some(String(x));
}
console.assert(Some(2).andThen(toString) === Some(2.toString()));
console.assert(None().andThen(toString) === None());

filter

Returns None if the option is None, otherwise calls predicate with the wrapped value and returns:

Some(t) if predicate returns true (where t is the wrapped value), an None if predicate returns false

function isEven(n: number): boolean {
  return n % 2 == 0;
}
console.assert(None().filter(isEven) === None());
console.assert(Some(3).filter(isEven) === None());
console.assert(Some(4).filter(isEven) === Some(4));

xor

Returns Some if exactly one of self, optb is Some, otherwise returns None.

insert

Inserts value into the option, then returns a mutable reference to it.

If the option already contains a value, the old value is dropped.

See also getOrInsert, which doesn’t update the value if the option already contains Some.

const opt = None();
const val = opt.insert(1);
console.assert(val === 1);
console.assert(opt.unwrap() === 1);
// another example
const val = opt.insert(2);
console.assert(val === 2);

replace

Replaces the actual value in the option by the value given in parameter, returning the old value if present, leaving a Some in its place without deinitializing either one.

const x = Some(2);
const old = x.replace(5);
console.assert(x === Some(5));
console.assert(old === Some(2));
// another example
const x = None();
const old = x.replace(3);
console.assert(x === Some(3));
console.assert(old === None());

zip

Zips self with another Option.

If self is Some(s) and other is Some(o), this method returns Some((s, o)). Otherwise, None is returned.

const x = Some(1);
const y = Some("hi");
const z = None<number>();

x.zip(y) === Some((1, "hi"));
x.zip(z) === None();

zipWith

Zips self and another Option with function f.

If self is Some(s) and other is Some(o), this method returns Some(f(s, o)). Otherwise, None is returned.

class Point {
  constructor(readonly x: number, readonly y: number) {}
  static create(x: number, y: number) {
    return new Point(x, y);
  }
}
const x = Some(17.5);
const y = Some(42.7);

x.zipWith(y, Point.create); // Some({ x: 17.5, y: 42.7 });

unzip

Unzips an option containing a tuple of two options.

If self is Some((a, b)) this method returns (Some(a), Some(b)). Otherwise, (None, None) is returned.

const x = Some([1, "hi"]);
const y = None<[number, number]>();
console.assert(x.unzip() === [Some(1), Some("hi")]);
console.assert(y.unzip() === [None(), None()]);

flatten

Converts from Option<Option<T>> to Option<T>.

const x: Option<Option<number>> = Some(Some(6));
Some(6) === x.flatten();

const x: Option<Option<number>> = Some(None());
None() === x.flatten();

const x: Option<Option<number>> = None();
None() === x.flatten();

isSome

Returns true if the option is a Some value.

const x: Option<number> = Some(2);
x.isSome() === true; // true

const x: Option<number> = None();
x.isSome() === false; // true

isNone

Returns true if the option is a None value.

isSomeAnd

Returns true if the option is a Some and the value inside of it matches a predicate.

const x: Option<number> = Some(2);
x.isSomeAnd((x) => x > 1) === true; // true

const x: Option<number> = Some(0);
x.isSomeAnd((x) => x > 1) === false; // true

const x: Option<number> = None();
x.isSomeAnd((x) => x > 1) === false; // true

getOrInsert

Inserts value into the option if it is None, then returns a mutable reference to the contained value.

See also insert, which updates the value even if the option already contains Some.

const x = None<number>();
const y = x.getOrInsert(7);

y === 7; // true

getOrInsertWith

Inserts a value computed from f into the option if it is None, then returns the contained value.

const x = None<number>();
const y = x.getOrInsertWith(() => 5);

y === 5; // true

or

Returns the Option if it contains a value, otherwise returns optb. Arguments passed to or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use orElse, which is lazily evaluated.

const x = Some(2);
const y = None();
console.assert(x.or(y) === Some(2));
// another example
const x = None();
const y = Some(100);
console.assert(x.or(y) === Some(100));
// another example
let x = Some(2);
let y = Some(100);
console.assert(x.or(y) === Some(2));
// another example
const x: Option<number> = None();
const y = None();
console.assert(x.or(y) === None());

orElse

Returns the Option if it contains a value, otherwise calls f and returns the result.

function nobody(): Option<string> {
  return None();
}
function vikings(): Option<string> {
  return Some("vikings");
}

Some("barbarians").orElse(vikings) === Some("barbarians"); // true
None().orElse(vikings) === Some("vikings"); // true
None().orElse(nobody) === None(); // true

Boolean Operators

These methods treat the Option as a boolean value, where Some acts like true and None acts like false. There are two categories of these methods: ones that take an Option as input, and ones that take a function as input (to be lazily evaluated).

The and, or, and xor methods take another Option as input, and produce an Option as output. Only the and method can produce an Option<U> value having a different inner type U than Option<T>.

method	self	input	output
and	None	(ignored)	None
and	Some(x)	None	None
and	Some(x)	Some(y)	Some(y)
or	None	None	None
or	None	Some(y)	Some(y)
or	Some(x)	(ignored)	Some(x)
xor	None	None	None
xor	None	Some(y)	Some(y)
xor	Some	None	Some(x)
xor	Some(x)	Some(y)	None

The andThen and orElse methods take a function as input, and only evaluate the function when they need to produce a new value. Only the andThen method can produce an Option<U> value having a different inner type U than Option<T>.

method	self	function input	function result	output
andThen	None	(not provided)	(not evaluated)	None
andThen	Some(x)	x	None	None
andThen	Some(x)	x	Some(y)	Some(y)
orElse	None	(not provided)	None	None
orElse	None	(not provided)	Some(y)	Some(y)
orElse	Some(x)	(not provided)	(not evaluated)	Some(x)

This is an example of using methods like andThen and or in a pipeline of method calls. Early stages of the pipeline pass failure values (None) through unchanged, and continue processing on success values (Some). Toward the end, or substitutes an error message if it receives None.

toString

Returns string representation of the Option value.

Some(3).toString(); // Some(3)
None(null).toString(); // None(null)

valueOf

Returns self value. Not recommended for use but can be useful in some cases.

Some(3).valueOf(); // 3
None(null).valueOf(); // null
None().valueOf(); // undefined
None("some string").valueOf(); // some string

toJSON

Returns JSON representation of the Option value. This method is used by JSON.stringify().

Not recommended for use but can be useful in some cases.

Some(1).toJSON(); // { status: 'Some', value: 1 };
None().toJSON(); // { status: 'None', value: undefined };
None(null).toJSON(); // { status: 'None', value: null };

Symbols

Symbol.toPrimitive

since 3.x.x

Returns value from Option

Symbol.toStringTag

since 3.x.x

Symbol.asyncIterator

since 3.x.x

See MDN docs for more

Note: This method will only yeild if the Option is Some

Note: throws UndefinedBehaviorError for Some(value) if value is not implements Symbol.asyncIterator

Symbol.iterator

since 3.x.x

See MDN docs for more

Note: This method will only yeild if the Option is Some

Note: throws UndefinedBehaviorError for Some(value) if value is not implements Symbol.iterator

Example:

const a = Some([1, 2, 3]);
for (const el of a) {
  console.log("element is:", el);
}
// will prints
// element is: 1
// element is: 2
// element is: 3

const b = Some(1);
// will throws, Symbol.iterator is not suported for number
for (const el of b) {
  console.log("element is:", el);
}

const c = Some({
  [Symbol.iterator]() {
    return 1;
  },
});

for (const el of c) {
  console.log("iterable:", el);
}
// will prints
// iterable: 1

Symbol.split

implemented since 3.x.x version

See MDN docs for more

NOTE: throws UndefinedBehaviorError if wrapped value is not a string or RegExp

example:

const a = Some("bar");

"foobar".split(a); // ["foo", ""]

Symbol.search

implemented since 3.x.x version

See MDN docs for more

NOTE: throws UndefinedBehaviorError if wrapped value is not a string or RegExp

Symbol.inspect

util.inspect is a server feature

The util.inspect() method returns a string representation of object that is intended for debugging.

See more about Symbol.inspect

Example:

import util from "node:util";

const a = Some(4);
util.inspect(a); // Some(4)

Result

Result<T, E> is the type used for returning and propagating errors. It is an enum with the variants, Ok(T), representing success and containing a value, and Err(E), representing error and containing an error value.

Functions

Ok(T)

Represents success with T value.

Ok function is also instance of Resultclass and Ok function.

const aOk = Ok(123);
const aErr = Err(123);

aOk instanceof Result; // true
aOk instanceof Ok; // true
aOk instanceof Err; // false

aErr instanceof Result; // true
aErr instanceof Ok; // false
aErr instanceof Err; // true

Err(E)

Represents fail with some error inside.

const aErr = Err(123);

aErr.isErr(); // true
aErr.unwrapErr(); // 123
aErr.unwrap(); // throws since aErr is Err

Err function is also instance of Resultclass and Err function.

const aErr = Err(123);
aErr instanceof Result; // true
aErr instanceof Err; // true
aErr instanceof Ok; // false

constructor(executor)

• executor - function that receives a some and none functions as arguments. Return value is used as Ok. If executor throws an error, it is used as Err.
  • ok(value) - function that receives a value and returns Ok(value)
  • err(reason) - function that receives a reason and returns Err(reason)

NOTE: Throws UndefinedBehaviorError if executor is not a function or executor returns a Promise or executor is async function

// normal function execution
const r1 = new Result(() => {
  throw new Error("qwe");
});
r1.isErr(); // true
r1.unwrapErr(); // Error('qwe')

const r2 = new Result(() => {
  return "some success";
});
r2.isOk(); // true
r2.unwrap(); // "some success"

// using control flow functions
const r3 = new Result((ok, err) => {
  // return is not needed
  Math.random() > 0.5 ? ok("success") : err("error");
});

// Note: async functions or Promise return will throw an error. use `fromPromise` or `fromAsync`
new Result(async () => {
  // throws
  await Promise.resolve();
});
new Result(() => Promise.resolve()); // throws
Result.fromPromise(Promise.resolve("okay")); // OK. Result<okay>

Static methods/fields

fromPromise/fromAsync

transforms given promise into a Result.

const r = await Result.fromPromise(Promise.resolve("okay"));
r.unwrap(); // okay

const r2 = await Result.fromPromise(Promise.reject("error"));
r2.unwrapErr(); // error

Status

Static property that returns object with all possible statuses.

withResolvers

Returns an object with option and ok, err functions. Similar to Promise.withResolvers

const { result, ok, err } = Result.withResolvers();

ok(2);
console.log(option.unwrap()); // 2

err("qwe"); // doing noting. result is already set to 2

is(value)

Returns true if the value is an instance of Result.

ok/Ok

returns Ok value if the value is an instance of Result. Same as Ok function.

err/Err

returns Err value if the value is an instance of Result. Same as Err function.

Methods/Fields

expect

Returns the contained Ok value, consuming the self value.

Because this function may throws, its use is generally discouraged. Call unwrapOr, unwrapOrElse.

Panics if the value is an Err, with a message including the passed message, and the content of the Err.

const x: Result<number, string> = Err("emergency failure");
x.expect("Testing expect"); // `Testing expect`, cause: emergency failure

unwrap

Returns the contained Ok value, consuming the self value.

Because this function may throws, its use is generally discouraged. Instead, call unwrapOr, unwrapOrElse.

const x: Result<number, string> = Ok(2);
x.unwrap() === 2;

unwrapOr

eturns the contained Ok value or a provided default.

Arguments passed to unwrapOr are eagerly evaluated; if you are passing the result of a function call, it is recommended to use unwrapOrElse, which is lazily evaluated.

const fallback = 2;
const x = Ok(9);
x.unwrapOr(fallback) === 9; // true

cosnt x: Result<number, string> = Err("error");
x.unwrapOr(fallback) === fallback; // true

isOk

Returns true if the result is Ok.

const x: Result<number, string> = Ok(-3);
x.isOk(); // true
// another example
let x: Result<number, string> = Err("Some error message");
x.isOk(); // false

isOkAnd

Returns true if the result is Ok and the value inside of it matches a predicate.

const x: Result<number, string> = Ok(2);
console.assert(x.isOkAnd((x) => x > 1) === true);
// another example
const x: Result<number, string> = Ok(0);
console.assert(x.isOkAnd((x) => x > 1) === false);
// another example
const x: Result<number, string> = Err("hey");
console.assert(x.isOkAnd((x) => x > 1) === false);

isErr

Returns true if the result is Err.

const x: Result<number, string> = Ok(-3);
console.assert(x.isErr() === false);
// another example
const x: Result<number, string> = Err("Some error message");
console.assert(x.isErr() === true);

isErrAnd

Returns true if the result is Err and the value inside of it matches a predicate.

const x: Result<number, Error> = Err(new Error("not found"));
x.isErrAnd((e) => e.message === "not found"); // true;
// another example
const x: Result<number, Error> = Err(new Error("permission denied"));
x.isErrAnd((x) => x.name === "TypeError"); // false
// another example
const x: Result<number, Error> = Ok(123);
x.isErrAnd((e) => e.name == "Error"); // false

ok

Converts self into an Option<T>, consuming self, and discarding the error, if any.

const x: Result<number, string> = Ok(2);
x.ok() === Some(2); // true
// another example
const x: Result<number, string> = Err("Nothing here");
x.ok() === None(); // true

err

Converts self into an Option<E>, consuming self, and discarding the success value, if any.

const x: Result<number, string> = Ok(2);
x.err() === None(); // true

const x: Result<number, string> = Err("Nothing here");
x.err() === Some("Nothing here"); // true

map

Maps a Result<T, E> to Result<U, E> by applying a function to a contained Ok value, leaving an Err value untouched.

This function can be used to compose the results of two functions.

const x = Ok(1);
x.map((v) => v * 2) === Ok(2); // true

mapOr

Returns the provided default (if Err), or applies a function to the contained value (if Ok),

Arguments passed to mapOr are eagerly evaluated; if you are passing the result of a function call, it is recommended to use mapOrElse, which is lazily evaluated.

const x: Result<string, string> = Ok("foo");
x.mapOr(42, (v) => v.length); // result is 3
// another example
const x: Result<number, string> = Err("bar");
x.mapOr(42, (v) => v.length); // 42

mapOrElse

Maps a Result<T, E> to U by applying fallback function default to a contained Err value, or function f to a contained Ok value.

This function can be used to unpack a successful result while handling an error.

let k = 21;

const x: Result<string, string> = Ok("foo");
x.mapOrElse(
  (err) => k * 2,
  (v) => v.length
); // 3

const y: Result<string, string> = Err("bar");
y.mapOrElse(
  (e) => k * 2,
  (v) => v.length
); // 42

mapErr

Maps a Result<T, E> to Result<T, F> by applying a function to a contained Err value, leaving an Ok value untouched.

This function can be used to pass through a successful result while handling an error.

const stringify = (x: number) => `error code: ${x}`;

const x: Result<number, number> = Ok(2);
x.mapErr(stringify) === Ok(2); // true

const y: Result<number, number> = Err(13);
y.mapErr(stringify) === Err("error code: 13");

expectErr

Returns the contained Err value, consuming the self value.

const x: Result<number, string> = Ok(10);
x.expectErr("Testing expectErr"); // throws `Testing expectErr; cause: 10`

unwrapErr

Returns the contained Err value, consuming the self value.

const x: Result<number, string> = Err("emergency failure");
x.unwrapErr() === "emergency failure";

unwrapOrElse

Returns the contained Ok value or computes it from a closure.

const count = (x: string) => x.length;

Ok(2).unwrapOrElse(count) === 2; // true
Err("foo").unwrapOrElse(count) === 3; // true

and

Returns res if the result is Ok, otherwise returns the Err value of self.

Arguments passed to and are eagerly evaluated; if you are passing the result of a function call, it is recommended to use andThen, which is lazily evaluated.

const x: Result<number, string> = Ok(2);
const y: Result<string, string> = Err("late error");
x.and(y) === Err("late error"); // true
// another example
const x: Result<number, string> = Err("early error");
const y: Result<string, string> = Ok("foo");
x.and(y) === Err("early error"); // true
// another example
const x: Result<number, string> = Err("not a 2");
const y: Result<string, string> = Err("late error");
x.and(y) === Err("not a 2"); // true
// another example
const x: Result<number, string> = Ok(2);
const y: Result<string, string> = Ok("different result type");
x.and(y) === Ok("different result type"); // true

andThen

Calls op if the result is Ok, otherwise returns the Err value of self.

This function can be used for control flow based on Result values.

const sqThenToString = (x: number) => {
    return Ok(x * x).map(sq => sq.toString())
}

Ok(2).andThen(sqThenToString) === Ok(4.toString())); // true
Err("not a number").andThen(sqThenToString) === Err("not a number"); // true

or

Returns res if the result is Err, otherwise returns the Ok value of self.

Arguments passed to or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use orElse, which is lazily evaluated.

const x: Result<number, string> = Ok(2);
const y: Result<number, string> = Err("late error");
x.or(y) === Ok(2); // true
// another example
const x: Result<number, string> = Err("early error");
const y: Result<number, string> = Ok(2);
x.or(y) === Ok(2); // true
// another example
const x: Result<number, string> = Err("not a 2");
const y: Result<number, string> = Err("late error");
x.or(y) === Err("late error"); // true
// another example
const x: Result<number, string> = Ok(2);
const y: Result<number, string> = Ok(100);
x.or(y) === Ok(2); // true

orElse

Calls fn if the result is Err, otherwise returns the Ok value of self.

This function can be used for control flow based on result values.

const sq = (x: number) => Ok(x * x);
const err = (x: number) => Err(x);

Ok(2).orElse(sq).orElse(sq) === Ok(2); // true
Ok(2).orElse(err).orElse(sq) === Ok(2); // true
Err(3).orElse(sq).orElse(err) === Ok(9); // true
Err(3).orElse(err).orElse(err) === Err(3); // true

flatten

Converts from Result<Result<T, E>, E> to Result<T, E>

const x: Result<Result<string, number>, number> = Ok(Ok("hello"));
Ok("hello") === x.flatten(); // true

const x: Result<Result<string, number>, number> = Ok(Err(6));
Err(6) === x.flatten(); // true

const x: Result<Result<string, number>, number> = Err(6);
Err(6) === x.flatten(); // true

Boolean Operators

These methods treat the Result as a boolean value, where Ok acts like true and Err acts like false. There are two categories of these methods: ones that take a Result as input, and ones that take a function as input (to be lazily evaluated).

The and and or methods take another Result as input, and produce a Result as output. The and method can produce a Result<U, E> value having a different inner type U than Result<T, E>. The or method can produce a Result<T, F> value having a different error type F than Result<T, E>.

method	self	input	output
and	Err(e)	(ignored)	Err(e)
and	Ok(x)	Err(d)	Err(d)
and	Ok(x)	Ok(y)	Ok(y)
or	Err(e)	Err(d)	Err(d)
or	Err(e)	Ok(y)	Ok(y)
or	Ok(x)	(ignored)	Ok(x)

The andThen and orElse methods take a function as input, and only evaluate the function when they need to produce a new value. The andThen method can produce a Result<U, E> value having a different inner type U than Result<T, E>. The orElse method can produce a Result<T, F> value having a different error type F than Result<T, E>.

method	self	function input	function result	output
andThen	Err(e)	(not provided)	(not evaluated)	Err(e)
andThen	Ok(x)	x	Err(d)	Err(d)
andThen	Ok(x)	x	Ok(y)	Ok(y)
orElse	Err(e)	e	Err(d)	Err(d)
orElse	Err(e)	e	Ok(y)	Ok(y)
orElse	Ok(x)	(not provided)	(not evaluated)	Ok(x)

toString

Returns string representation of the Result value.

Ok(3).toString(); // Ok(3)
Err(null).toString(); // Err(null)

valueOf

Returns self value. Not recommended for use but can be useful in some cases.

Ok(3).valueOf(); // 3
Err(null).valueOf(); // null
Err("qwe").valueOf(); // qwe

toJSON

Returns JSON representation of the Result value. This method is used by JSON.stringify().

Not recommended for use but can be useful in some cases.

Ok(1).toJSON(); // { status: 'Ok', value: 1 };
Err(null).toJSON(); // { status: 'Err', value: null };
Err("qwe").toJSON(); // { status: 'Err', value: 'qwe' };

Symbols

Symbol.toPrimitive

Symbol.toStringTag

Symbol.iterator

since 3.x.x

See MDN docs for more

Note: This method will only yeild if the Option is Some

Note: throws UndefinedBehaviorError for Ok(value) if value is not implements Symbol.iterator

Err value is not iterable.

Example:

const a = Ok([1, 2, 3]);
for (const el of a) {
  console.log("element is:", el);
}
// will prints
// element is: 1
// element is: 2
// element is: 3

const b = Ok(1);
// will throws, Symbol.iterator is not suported for number
for (const el of b) {
  console.log("element is:", el);
}

const c = Ok({
  [Symbol.iterator]() {
    return 1;
  },
});

for (const el of c) {
  console.log("iterable:", el);
}
// will prints
// iterable: 1

Symbol.asyncIterator

since 3.x.x

See MDN docs for more

Note: This method will only yeild if the Option is Some

Note: throws UndefinedBehaviorError for Some(value) if value is not implements Symbol.asyncIterator

Symbol.split

since 3.x.x

Symbol.search

since 3.x.x

Symbol.inspect

since 3.x.x

util.inspect is a node.js feature. See util.inspect docs

The util.inspect() method returns a string representation of object that is intended for debugging.

Example:

import util from "node:util";

const a = Ok(4);
util.inspect(a); // Ok(4)
util.inspect(Err("some error")); // Err('some error')