Working with Javascript objects

Jan 6 2023

default

This snippet assigns default values for all properties in an object that are undefined.

const defaults = (obj, ...defs) =>
  Object.assign({}, obj, ...defs.reverse(), obj)

defaults({ a: 1 }, { b: 2 }, { b: 6 }, { a: 3 }) // { a: 1, b: 2 }

findKey

This snippet returns the first key that satisfies a given function.

const findKey = (obj, fn) =>
  Object.keys(obj).find((key) => fn(obj[key], key, obj))

findKey(
  {
    barney: { age: 36, active: true },
    fred: { age: 40, active: false },
    pebbles: { age: 1, active: true },
  },
  (o) => o['active']
) // 'barney'

forOwn

This snippet iterates on each property of an object and iterates a callback for each one respectively.

const forOwn = (obj, fn) =>
  Object.keys(obj).forEach((key) => fn(obj[key], key, obj))
forOwn({ foo: 'bar', a: 1 }, (v) => console.log(v)) // 'bar', 1

isObject

This snippet can be used to check whether a provided value is an object. It uses the Object constructor to create an object wrapper for the given value. If it is already an object, then an object type that corresponds to the given value will be returned. Otherwise, a new object will be returned.

const isObject = (obj) => obj === Object(obj)

isObject([1, 2, 3, 4]) // true
isObject([]) // true
isObject(['Hello!']) // true
isObject({ a: 1 }) // true
isObject({}) // true
isObject(true) // false

isObjectLike

This snippet can be used to check if a value is not null and that its typeof is “object”.

const isObjectLike = (val) => val !== null && typeof val === 'object'

isObjectLike({}) // true
isObjectLike([1, 2, 3]) // true
isObjectLike((x) => x) // false
isObjectLike(null) // false

isPlainObject

This snippet checks whether a value is an object created by the Object constructor.

const isPlainObject = (val) =>
  !!val && typeof val === 'object' && val.constructor === Object

isPlainObject({ a: 1 }) // true
isPlainObject(new Map()) // false

matches

This snippet compares two objects to determine if the first one contains the same property values as the second one.

const matches = (obj, source) =>
  Object.keys(source).every(
    (key) => obj.hasOwnProperty(key) && obj[key] === source[key]
  )

matches({ age: 25, hair: 'long', beard: true }, { hair: 'long', beard: true }) // true
matches({ hair: 'long', beard: true }, { age: 25, hair: 'long', beard: true }) // false

shallowClone

This snippet can be used to create a shallow clone of an object.

const shallowClone = (obj) => Object.assign({}, obj)

const a = { x: true, y: 1 }
const b = shallowClone(a) // a !== b

Create an empty object without any inheritance

const a = Object.create(null)

Check if an object is empty

const isEmpty = (obj) =>
  Reflect.ownKeys(obj).length === 0 && obj.constructor === Object