While writing a redux reducer I ran into the issue that I wanted to remove a property from an object without mutating it. Here's how I solved it. tl;dr Just use http://devdocs.io/lodash/index#omit #redux #reducers #immutability

immutable-delete.js

import test from 'ava'
import deepFreeze from 'deep-freeze'
import omit from 'lodash/omit'

test('normal delete will mutate the object', t => {
  const obj = { a: 1, b: 2 }
  deepFreeze(obj)
  t.throws(() => delete obj.a)
})

test('naive implementation #1', t => {
  function immutableDelete (obj, prop) {
    const obj2 = {}
    Object.keys(obj)
      .filter(key => key !== prop)
      .forEach(key => obj2[key] = obj[key])
    return obj2
  }

  const obj = { a: 1, b: 2 }
  deepFreeze(obj)
  const obj2 = immutableDelete(obj, 'a')
  t.same(obj2, { b: 2 })
})

test('naive implementation #2', t => {
  function immutableDelete (obj, prop) {
    return Object.keys(obj)
      .filter(key => key !== prop)
      .reduce((obj2, key) => {
        obj2[key] = obj[key]
        return obj2
      }, {})
  }

  const obj = { a: 1, b: 2 }
  deepFreeze(obj)
  const obj2 = immutableDelete(obj, 'a')
  t.same(obj2, { b: 2 })
})

test('ah I can just use _.omit', t => {
  const obj = { a: 1, b: 2 }
  deepFreeze(obj)
  const obj2 = omit(obj, 'a')
  t.same(obj2, { b: 2 })
})