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The JavaScript Interview Handbook: 100+ Interview Questions

Challenge: Let's Add Properties

Explore how to convert an impure function into a pure function that returns a new object with additional properties without modifying the original. This lesson helps you understand immutability and functional programming principles in JavaScript through a hands-on challenge.

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Problem statement #

Study the code below and then run it.

Javascript (babel-node)
const func = (key, value, object) => {
  object[key] = value;
};
function test() {
  const car = {
    name: "Toyota"
  };
  const answer = func("model", 88, car);
  console.log({ car, answer });
}
test();

func is an impure function. The reasoning ...