m-o

A collection of functions that work on both Maps and Objects, letting you write code that can handle either, if that’s your M.O.

The functions are: has, hasIn, get, getIn, set, edit, delete, construct, reconstruct, entries, entriesArray, keys, keysArray, values, and valuesArray.

Installation

Requires Node.js 7.0.0 or above.

npm install m-o --save

The module exports an object with multiple methods.

Usage

Nota Bene: Maps can accept keys of any type, but Objects cannot. If you expect your code to work with both, then you should only use strings/numbers/symbols as keys.

const mo = require('m-o')
 
const map = new Map()
const obj = {}
 
// Set
mo.set(map, 'hello', 'world')
mo.set(obj, 'hello', 'world')
 
// Has
mo.has(map, 'hello') // true
mo.has(obj, 'hello') // true
 
// Get
mo.get(map, 'hello') // 'world'
mo.get(obj, 'hello') // 'world'
 
// vs. the normal way:
map.get('hello') // 'world'
obj.hello // 'world'
 
// Edit
mo.edit(map, 'hello', value => value + '!')
mo.edit(obj, 'hello', value => value + '!')
mo.get(map, 'hello') // 'world!'
mo.get(obj, 'hello') // 'world!'
 
// Delete
mo.delete(map, 'hello') // true
mo.delete(obj, 'hello') // true
mo.delete(map, 'nonexistent') // false
mo.delete(obj, 'nonexistent') // false
 
// Entries
mo.entries(map) // MapIterator
mo.entries(obj) // ArrayIterator
 
// Construct a Map or an Object, depending on the class provided
const entries = [['hello', 'world']]
mo.construct(Object, entries) // {hello: 'world'}
mo.construct(Map, entries) // Map
class XMap extends Map {}
mo.construct(XMap, entries) // XMap
 
// Construct a new Map or Object having the same class as an existing object
mo.reconstruct(obj, entries) // {hello: 'world'}
mo.reconstruct(map, entries) // Map
mo.reconstruct(new XMap(), entries) // XMap

Entries, Keys, and Values

The Map prototype has entries(), keys(), and values() methods which return iterators, whereas the global functions Object.entries(), Object.keys(), and Object.values() return arrays. The m-o module lets you remain consistent regardless of which type you’re dealing with. Use the entries(), keys(), and values() methods if you want iterators, and use entriesArray(), keysArray(), and valuesArray() if you want arrays.

Accessing Prototype Properties

By default, has and get treat an object like a dictionary and therefore only access its own properties. If you want to access object prototype properties as well, use the hasIn or getIn methods instead. (With Maps, behavior is the same regardless of which set of methods you use.)

typeof obj.toString // 'function'
typeof mo.get(obj, 'toString') // 'undefined'
typeof mo.getIn(obj, 'toString') // 'function'
 
mo.has(obj, 'toString') // false
mo.hasIn(obj, 'toString') // true