@cubux/readonly-set

A bunch of helper functions to work with read-only sets. Works internally with native sets without any kind of magic.

import { add, remove } from '@cubux/readonly-set';

const input: ReadonlySet<number> = new Set([10, 20, 30]);

console.log(add(input, 40));
// => Set(4) { 10, 20, 30, 40 }

console.log(remove(input, 20));
// => Set(2) { 10, 30 }

Alternative usage:

import * as RoSet from '@cubux/readonly-set';

const input: ReadonlySet<number> = new Set([10, 20, 30]);
console.log(RoSet.add(input, 40));
// => Set(4) { 10, 20, 30, 40 }

Use Cases

State management

import { FC, useState, ChangeEvent } from 'react';
import { toggle } from '@cubux/readonly-set';

const TodoList: FC = () => {
  const [checked, setChecked] = useState<ReadonlySet<string>>(() => new Set());

  const handleCheckItem = (key: string, e: ChangeEvent<HTMLInputElement>) =>
    setChecked(prev => toggle(prev, key, e.target.checked));

  ...
};

Install

npm i @cubux/readonly-set

API

add()

Add item to set

add(
  set: ReadonlySet<K>,
  key: K,
): ReadonlySet<K>

Creates new set from input set by adding item key.

• Will return input set when key is already included.

const input: ReadonlySet<number> = new Set([10, 20, 30]);

add(input, 40);
// => Set(4) { 10, 20, 30, 40 }

See also: toggle(), union().

intersection()

Intersection of sets

intersection(
  set:    ReadonlySet<K>,
  ...and: ReadonlySet<K>[],
): ReadonlySet<K>

Creates new set containing only items which are presented in all given sets.

• Will return input set when nothing to change (t.i. when set is a subset of every and sets).
• May return earlier when intermediate result is already empty set.

const input: ReadonlySet<number> = new Set([10, 20, 30, 40]);

intersection(input, new Set([30, 42, 20]));
// => Set(2) { 20, 30 }

See also subtract(), union().

remove()

Remove item from set

remove(
  set: ReadonlySet<K>,
  key: K,
): ReadonlySet<K>

Creates new set from set without given item key.

• Will return input set when key is not included in set.

const input: ReadonlySet<number> = new Set([10, 20, 30]);

console.log(remove(input, 20));
// => Set(2) { 10, 30 }

See also add(), intersection(), toggle().

subtract()

Subtract sets

subtract(
  set:    ReadonlySet<K>,
  ...sub: ReadonlySet<K>[]
): ReadonlySet<K>

Creates new set from set by subtracting every given sub set.

• Will return input set when nothing to change (t.i. when set doesn't include any item of any sub sets).
• May return earlier when intermediate result is already empty set.
• Logic of subtract(a, b, c) is same as subtract(subtract(a, b), c) and is same as subtract(a, union(b, c)).

const input: ReadonlySet<number> = new Set([10, 20, 30, 40]);

subtract(input, new Set([30, 42, 20]));
// => Set(2) { 10, 40 }

See also intersection(), remove().

syncFrom()

syncFrom(
  prev: ReadonlySet<K>,
  next: ReadonlySet<K>,
): ReadonlySet<K>

Returns prev when its elements are equal to elements in next (order does not matter). Otherwise, returns next.

toggle()

Toggle an item in set

toggle(
  set:           ReadonlySet<K>,
  key:           K,
  toBeIncluded?: boolean,
): ReadonlySet<K>

Creates new set from input set by either adding or removing item key with respect to optional flag toBeIncluded.

• If toBeIncluded is undefined (by default), it works as !set.has(key), t.i. key will be added if set doesn't include it, or removed otherwise. So, the result is always a new set in this case.
• If toBeIncluded is defined, it causes toggle() to work as either add() when toBeIncluded is true, or as remove() otherwise. In this case toggle() may return input set when nothing to change.

const input: ReadonlySet<number> = new Set([10, 20, 30]);

console.log(toggle(input, 20));
console.log(toggle(input, 20, false));
// both => Set(2) { 10, 30 }

console.log(toggle(input, 40));
console.log(toggle(input, 40, true));
// both => Set(4) { 10, 20, 30, 40 }

console.log(toggle(input, 20, true));
console.log(toggle(input, 40, false));
// both => Set(3) { 10, 20, 30 }

See also add(), remove().

union()

Union of sets

union(
  set:    ReadonlySet<K>,
  ...add: ReadonlySet<K>[],
): ReadonlySet<K>

Creates new set which includes items from all the given sets.

• Will return input set when nothing to change (t.i. when set is a superset of every sub sets).

const input: ReadonlySet<number> = new Set([10, 20, 30]);

union(input, new Set([30, 42, 20, 40]));
// => Set(5) { 10, 20, 30, 42, 40 }

See also add().