Javascript copy vs ref

Index.js

const a = { byId: {} }

// b is a reference to a, any change on a will mutate b
const b = a

// c is shallow copy of a, any change on the top level properties of a will not affect c although any change of nested object would affect c, if we mutate byId in a it will update byId in c
const c = { ...a }
//or
const cprime = Object.assign({}, a)

// d is a deep copy of a, any change in a wont affect d.
const d = JSON.parse(JSON.stringify(a))
// There are nicer way to deeply copy an object, for example one could use Lodash deepClone operator.

// With lodash
const e = _.deepClone(a)