Why do we needed pickBy in Lodash when We can use delete operator instead?

Question

I have a small question.

Why do we needed pickBy in Lodash or similar? Just simple with delete operator.

// Input
const source = {
  user: {
    firstname: "John",
    lastname: "Done"
  },
  password: "123"
};

// Output
const result = {
  user: {
    firstname: "John",
    lastname: "Done"
  }
};

There are many ways to get the desired result: https://codesandbox.io/s/cool-rubin-xlj25k?file=/src/index.ts

With pickBy:

const result = _.pickBy(
  source,
  (value, key) => !(key === "password" && value === "123")
);

With native:

const result = Object.fromEntries(
  Object.entries(source).filter(
    ([key, value]) => !(key === "password" && value === "123")
  )
);

And with delete operator: Lightweight, fastest, no loop,...vv

const result = Object.assign({}, source);
if (result.password === "123") {
  delete result.password;
}

So, I'm looking for reasons not to use delete operator.

---

--UPDATED for mutation issue:

All ways are mutated user.firstname

source.user.firstname = "New first name";
console.log({ source, result  });

{
  "source": {
    "user": {
      "firstname": "New first name",
      "lastname": "Done"
    },
    "password": "123"
  },
  "result": {
    "user": {
      "firstname": "New first name",
      "lastname": "Done"
    }
  }
}

Answer 1

Lightweight, fastest, no loop,...vv

Sure, if you're deleting a single key, use delete.

pickBy, as the name implies, is meant for predicate-function-based picking (filtering) of items, which is not what delete does without a loop.

For instance, if your (fictitious) goal is to turn

{
  "foo": "bar",
  "baz": "quux",
  "beq": "berp",
  "uub": "uuzpq",
}

into

{
  "beq": "berp",
  "uub": "uuzpq",
}

i.e. where the key and value start with the same letter – who knows why you'd need that but that's beside the point, you'd have a worse time with a loop and delete than with pickBy.