sg deepClone

index.js

/*
Write a function called deepClone which takes an object and creates a copy of it. e.g. {name: "Paddy", address: {town: "Lerum", country: "Sweden"}} -> {name: "Paddy", address: {town: "Lerum", country: "Sweden"}}
*/

const deepClone = entity => {
  if (entity === null) {
    return null
  }
  if (entity instanceof Function) {
    return entity
  }
  if (typeof entity !== "object") {
    return entity
  }
  if (entity instanceof Array) {
    return entity.map(item => deepClone(item))
  }
  const result = {}
  for (const key in entity) {
    result[key] = deepClone(entity[key])
  }
  return result
}

const run = () => {
  const entity = {name: "Paddy", address: {town: "Lerum", country: "Sweden"}}
  console.log(JSON.stringify(entity, null, 2))
  console.log("--->")
  console.log(JSON.stringify(deepClone(entity), null, 2))
}

const test = () => {
  const assert = condition => {
    if (!condition) {
      throw new Error("test failed")
    }
    console.log("test passed")
  }

  // this demonstrates the copy is complete, meaning the clone has the exact same set of data
  const testCompleteness = () => {
    assert(deepClone(null) === null)
    assert(deepClone(undefined) === undefined)
    assert(deepClone() === undefined)
    assert(deepClone(1) === 1)
    assert(deepClone("abc") === "abc")
    assert(deepClone(() => "abc")() === "abc")
    {
      const entity = [1, 2, 3]
      assert(JSON.stringify(deepClone(entity)) === JSON.stringify(entity))
      assert(deepClone(entity)[0] === 1)
      assert(deepClone(entity)[1] === 2)
      assert(deepClone(entity)[2] === 3)
      assert(deepClone(entity).length === 3)
    }
    {
      const entity = { a: 1, b: 2, c: 3 }
      assert(JSON.stringify(deepClone(entity)) === JSON.stringify(entity))
      assert(deepClone(entity).a === 1)
      assert(deepClone(entity).b === 2)
      assert(deepClone(entity).c === 3)
      assert(Object.keys(deepClone(entity)).length === 3)
    }
    {
      const entity = [{doer: () => "value"}]
      assert(deepClone(entity)[0].doer() === "value")
    }
  }

  // this demonstrates it is indeed a separate copy, meaning changing one won't impact the other
  const testSeparateCopy = () => {
    {
      const entity = [1]
      const clone = deepClone(entity)
      clone[0] = 2
      assert(clone[0] === 2)
      assert(entity[0] === 1)
    }
    {
      const entity = { a: 1 }
      const clone = deepClone(entity)
      clone.a = 2
      assert(clone.a === 2)
      assert(entity.a === 1)
    }
  }

  testCompleteness()
  testSeparateCopy()
}

run()
test()