3fn

Three-Way Comparison Function (3fn)

Creates a callback that compares two objects by one or more keys.

Installation

Requires Node.js 8.3.0 or above.

npm i 3fn

API

The module exports a single function.

Parameters

1. Variadic/Optional: sortBy (function, array, or any): A Map/object key. An array will be interpreted as a chain of nested keys. A function will be interpreted as a three-way comparison callback that accepts two arguments and returns a number. If the key is user-provided, you should wrap it in an array; otherwise you’ll have problems if the key is a function, array, or plain object.
2. Optional: options (plain object): An argument passed to the 3 and kget modules, allowing you to set their options. The most commonly-needed option is inObj, which must be set to true if sortBy is a key which points to an inherited object property.

Return Value

A callback function that accepts a Map, Object, or other collection as its argument and returns -1, 0, or 1. This callback then can be passed to the sort function of an Array, for example.

Examples

Compare By Key

const threeFn = require('3fn')

const personA = {name: 'John'}
const personB = {name: 'Andrew'}

const compare = threeFn('name')

compare(personA, personB) // 1
compare(personB, personA) // -1

[personA, personB].sort(compare) // [personB, personA]

Compare By Inherited Key

const threeFn = require('3fn')

const _name = Symbol('name')

class Person {
  constructor (name) {
    this[_name] = name
  }

  get name () {
    return this[_name]
  }
}

const personA = new Person('John')
const personB = new Person('Andrew')

const compare = threeFn('name', {inObj: true})

compare(personA, personB) // 1
compare(personB, personA) // -1

[personA, personB].sort(compare) // [personB, personA]

Compare By Multiple Keys

const threeFn = require('3fn')

const personA = {name: 'John', age: 46}
const personB = {name: 'John', age: 27}

const compare = threeFn('name', 'age') // Sort by name first, and by age second

compare(personA, personB) // 1
compare(personB, personA) // -1

[personA, personB].sort(compare) // [personB, personA]

Compare By Nested Keys

const threeFn = require('3fn')

const personA = {name: {first: 'John'}}
const personB = {name: {first: 'Andrew'}}

const compare = threeFn(['name', 'first'])

compare(personA, personB) // 1
compare(personB, personA) // -1

[personA, personB].sort(compare) // [personB, personA]

Related

This module is based on 3, the three-way comparison module.

It is also part of the fn family of modules:

• efn: Extracted Function
• ffn: Filtering Function
• jfn: Joined Function
• mfn: Memoized Function
• ofn: Overloaded Function
• pfn: Possible Function
• qfn: Qualified Function
• vfn: Variadic Function
• wfn: Wrapper Function
• xfn: Extended Function