@jemmyphan/optional-chain

optional-chain

Optional chaining implementation in TypeScript.
Uses option type

Requirement

This library requires TS 2.8+ version to use conditional type

Install

npm install optional-chain

Usage

import { optional } from "optional-chain";

type User = {
  name?: {
    first: string
  }
}
const user: User = getUser(); // { name: null }
const optionalUser = optional(user);
optionalUser.k("name").k("first").get(); // undefined, does not throw an exception.

API

optional-chain library exports below APIs.

optional

optional is a fuctory function to creates a Option instance.

Option<T>

An instance of Option can be constructed with a value for the souce of T. Option class can hold a type of Some or None based on given source.

.k(name: string)

type User = {
  name: string;
  sns: SNS;
  followers: User[];
};

type SNS = {
  twitter?: {
    username: string;
  };
  facebook?: {
    url: string;
  };
};

const user: User = {
  name: "yayoc",
  sns: {
    twitter: {
      username: "@yayoc_"
    }
  },
  followers: []
};
const optionalUser = optional(user);
optionalUser.k("name"); // Option<string>
optionalUser.k("sns"); // Option<{twitter: { username: string }}>
optionalUser.k("sns").k("facebook"); // None
optionalUser.k("foo"); // compile error

Returns a Option<T> narrowed by specified property of Object.

.i(index: number)

Returns a Option<T> narrowed by specified index of Array. If index is not in array, this returns Option<undefined>.

optionalUser
  .k("followers")
  .i(0)
  .k("name"); // None

.get()

Returns a value of Option.

optionalUser.k("name").get(); // yayoc

.match({ some: T => any, none: T => any })

A public method of Option to do pattern matching. If target Option is Some type, this funciton returns a result of given some function. Otherwise, this function returns a result of given none function.

optionalUser
  .k("sns")
  .k("twitter")
  .match({
    some: v => v,
    none: v => `there is no account: ${v}`
  }); // @yayoc_

.getOrElse(value: any)

A public method to return T value when the instance contains some value. Otherwise, this function will return given value.

optionalUser
  .k("sns")
  .k("facebook")
  .k("url")
  .getOrElse("https://facebook.com"); // https://facebook.com

Credits

This library is highly inspired by lens.ts @utatti created.

License

MIT