alexnault

// mutable
const bands = ["Metallica", "Queen"];
bands.push("Nirvana");

// immutable
const someBands = ["Metallica", "Queen"];
const bands = [...someBands, "Nirvana"];

alexnault

// impure (using side effect instead of return value)
function addTaco(array) {
   array.push("taco");
}

// impure (using shared variable instead of argument)
function addTaco() {
   return [...globalArray, "taco"];
}

alexnault

const names = ["Han", "Chewbacca", "Luke", "Leia"];

// imperative
const shortNames = [];
for (let i = 0; i < names.length; i++) {
   if (names[i].length < 5) {
      shortNames.push(names[i]);
   }
}