Discussion on: Pure Functions Explained for Humans

[Sergey Konik]

Thank you for the article. Brings some clarity regarding code quality.

Can we consider functions that return new objects with updated properties as pure?
e.g

user = {
   username: "jack",
};

function updateUsername(user, new_username) {
  return {
    ...user,
    username: new_username,
  }
};

user = updateUsername(user, "tester");
// user { username: "tester" }

What do you think?

[Ashik Al Abdullah]

From what I understood, this function would be impure. Because, here, user object is an input for the method. And inside the updateUsername(), we are mutating its value. According to this blog, the function will become impure if we mutate the input.