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Pure Functions & Immutability — Series 2

Preview — 3 of 10 questions

Which of the following best describes a pure function?

AA function that, given the same inputs, always returns the same output and produces no observable side effects

BA function that always returns undefined

CA function that only accepts a single argument

DA function declared with the function keyword rather than as an arrow function

What is logged, and is addToTotal a pure function?

javascript

let total = 0;

function addToTotal(n) {
  total += n;
  return total;
}

console.log(addToTotal(5));
console.log(addToTotal(5));

A5, 5 — pure, since it always returns 5 for the input 5

B5, 10 — not pure, because it mutates and depends on external state

C5, 10 — still pure, since it only reads total internally

D10, 10 — pure

What is logged?

javascript

const numbers = Object.freeze([1, 2, 3]);

try {
  numbers.push(4);
} catch (e) {
  console.log(e instanceof TypeError);
}

console.log(numbers.length);
console.log(numbers);

Afalse, 4, [1, 2, 3, 4]

Bfalse, 3, [1, 2, 3]

Ctrue, 3, [1, 2, 3]

Dtrue, 4, [1, 2, 3, 4]

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