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Discussion on: Pure Functions Explained for Humans

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skonik profile image
Sergey Konik • • Edited

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" }
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What do you think?

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ashik224 profile image
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.

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strongunsullied profile image
Kasope Johnson •

Agreed. It would be pure if the function created a clone of the object and then mutated that