result-js

The standard API for result in JavaScript.

What

It brings a standard Result representation to the JavaScript world.

Provides an API for complete representation of two states representing success and failure.

Our goal is to become the standard error handling method for third-party libraries.

It has the following features:

Simple and lean

Designed to be used as client JavaScript (Off Course server side). It provides an API that is as small and lean as possible. There is not a single useless API for you to use.
Ok and Err

The Result consists of two containers, Ok and Err. The naming is inspired by Rust::std:Result and is short and easy to understand.
Self-contained

Result is self-contained. This means that type declarations, container creation, retrieval of values from containers, and comparison of container types are provided by Result.

If you want to know more, see Definition.

What is not

Client JavaScript is a special execution environment. Unnecessary API bloat is reflected in bundle size, to the detriment of users.

Unfortunately, being a dynamic language, JavaScript tree-shaking has its limitations.

Therefore, intentionally, it does not have the following features.

Monad laws
Rust::std::result like

These may include some APIs that are not used for all libraries.

Create Ok(success) container

Ok container is created with Result#ok. Accepts any value.

import { Result } from "https://deno.land/x/result_js@$VERSION/mod.ts";
const result = Result.ok("any success value");

Create Err(failure) container

Err container is created with Result#err. Accepts any value.

import { Result } from "https://deno.land/x/result_js@$VERSION/mod.ts";
const result = Result.err("any error value");

Define a container as the return value

The Result defines OK on the left and error on the right.

import { Result } from "https://deno.land/x/result_js@$VERSION/mod.ts";

function div(left: number, right: number): Result<number, RangeError> {
  if (right === 0) {
    return Result.err(new RangeError("Division by zero"));
  }
  return Result.ok(left / right);
}

Retrieving values from containers

The container has a type that represents the type of its own container. This allows you to identify Ok containers and Err containers.

import { Result } from "https://deno.land/x/result_js@$VERSION/mod.ts";
declare const result: Result<number, RangeError>;

if (result.type === "ok") {
  result.value;
} else {
  result.value;
}

These are all the functions of a container.

Handle dangerous code

Wrap code that may throw errors in a container.

import { unsafe } from "https://deno.land/x/result_js@$VERSION/mod.ts";
import { assertEquals } from "https://deno.land/std@$VERSION/testing/asserts.ts";

const result = unsafe(() => {
  throw Error("Dangerous!!");
});
assertEquals(result.value, Error());
assertEquals(result.type, "err");

By default, the Err container value is of type unknown. If you know more about the error being thrown, you can give a more detailed type.

For example, instantiation of Headers is known to throw TypeError.

import { unsafe } from "https://deno.land/x/result_js@$VERSION/mod.ts";
import { assertEquals } from "https://deno.land/std@$VERSION/testing/asserts.ts";

const result = unsafe<Headers, TypeError>(() =>
  new Headers({ "?": "invalid field name" })
);
assertEquals(result.value, new TypeError());

You would have wanted to specify only the type of error. unsafe<TypeError>(() => new Headers()); Unfortunately, this is not possible. TypeScript will only allow partial generics to be specified if The remaining generics become default type arguments. For that reason, unsafe accepts the type Ok on the left and Err on the right.

Pattern matching

It provides an interface similar to pattern matching in functional programming languages.

import { match, Result } from "https://deno.land/x/result_js@$VERSION/mod.ts";
import { assertEquals } from "https://deno.land/std@$VERSION/testing/asserts.ts";

const value = match(Result.ok("Tom"), {
  ok: (value) => "Hello " + value,
  err: (value) => "Goodby " + value,
});
assertEquals(value, "Hello Tom");

Validate container

Provides a function to check the type of container with Type guard.

isOk

Whether the ResultContainer is OkContainer or not.

import { isOk, Result } from "https://deno.land/x/result_js@$VERSION/mod.ts";
import { assertEquals } from "https://deno.land/std@$VERSION/testing/asserts.ts";

assertEquals(isOk(Result.ok("OK!!")), true);
assertEquals(isOk(Result.err("Error!!")), false);

isErr

Whether the ResultContainer is ErrContainer or not.

import { isErr, Result } from "https://deno.land/x/result_js@$VERSION/mod.ts";
import { assertEquals } from "https://deno.land/std@$VERSION/testing/asserts.ts";

assertEquals(isErr(Result.err("Error!!")), true);
assertEquals(isErr(Result.ok("OK!!")), false);

API

All APIs can be found in the deno doc.

License

Released under the MIT license

Inspired by Rust, Result.