Find differences between two objects

Object.diff.js

const contains = (key, list) => {
  return list.indexOf(key) > -1;
}

const diff = (first, second) => {
	let firstKeys = Object.keys(first);
	let secondKeys = Object.keys(second);
	let addition = secondKeys.filter(key => !contains(key, firstKeys))
	let deletion = firstKeys.filter(key => !contains(key, secondKeys))
	return {addition, deletion}
}