equatable

equatable

NOTE: equatable has been deprecated in favor of @esfx/equatable, @esfx/equatable-shim, and @esfx/collections. Please update your references.

The equatable package provides a low level API for defining equality.

Installation

npm i equatable

Usage

Basic Usage

import { Equatable, Equaler, Comparable, Comparer } from "equatable";

class Person {
    constructor(firstName, lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    toString() {
        return `${this.firstName} ${this.lastName}`;
    }

    [Equatable.equals](other) {
        return other instanceof Person
            && this.lastName === other.lastName
            && this.firstName === other.firstName;
    }

    [Equatable.hash]() {
        return Equaler.defaultEqualer.hash(this.lastName)
             ^ Equaler.defaultEqualer.hash(this.firstName);
    }

    [Comparable.compareTo](other) {
        if (!(other instanceof Person)) throw new TypeError();
        return Comparer.defaultComparer.compare(this.lastName, other.lastName)
            || Comparer.defaultComparer.compare(this.firstName, other.firstName);
    }
}

const people = [
    new Person("Alice", "Johnson")
    new Person("Bob", "Clark"),
];
people.sort(Comparer.defaultComparer.compare);
console.log(people); // Bob Clark,Alice Johnson

const obj1 = new Person("Bob", "Clark");
const obj2 = new Person("Bob", "Clark");
obj1 === obj2; // false
Equaler.defaultEqualer.equals(obj1, obj2); // true

Collections

This package includes a module of collection types in equatable/collections that can leverage these low level APIs:

HashSet/HashMap

import { HashSet } from "equatable/collections";

// NOTE: see definition of Person above
const obj1 = new Person("Bob", "Clark");
const obj2 = new Person("Bob", "Clark");

const set = new Set(); // native ECMAScript Set
set.add(obj1);
set.add(obj2);
set.length; // 2

const hashSet = new HashSet();
hashSet.add(obj1);
hashSet.add(obj2);
hashSet.length; // 1

SortedSet/SortedMap

import { SortedSet } from "equatable/collections";

// NOTE: see definition of Person above
const obj1 = new Person("Alice", "Johnson");
const obj2 = new Person("Bob", "Clark");

// ECMAScript native set iterates in insertion order
const set = new Set(); // native ECMAScript Set
set.add(obj1);
set.add(obj2);
[...set]; // Alice Johnson,Bob Clark

// SortedSet uses Comparable.compareTo if available
const sortedSet = new SortedSet();
sortedSet.add(obj1);
sortedSet.add(obj2);
[...sortedSet]; // Bob Clark,Alice Johnson

Global Shim

The global shim adds a default implementation of Equatable to Object.prototype and default implementations of Comparable to String.prototype, Number.prototype, Boolean.prototype, and BigInt.prototype.

To install the global shim, import equatable/global:

import "equatable/global"; // triggers global-scope side effects
import { Equatable } from "equatable";

123[Equatable.hash]() // 123