js-rest-parameter.js

// ************************************************
// ************** Rest parameter ******************
// ************************************************

// Reminder: 'arguments' represents a special array-like object that contains all arguments by their index.

function add1() {
  let sum = 0;
  for (let i = 0; i < arguments.length; i++) {
    sum += arguments[i];
  }
  return sum;
}

add1(); // 0
add1(1); // 1
add1(1, 2, 5, 8); // 16

function add2() {
  return arguments.reduce((sum, next) => sum + next);
}

add2(1, 2, 3); // TypeError: arguments.reduce is not a function

// use spread to turn arguments into array so we can apply array methods on them
function add3(...args) {
  return args.reduce((sum, next) => sum + next);
}

add3(1, 2, 3); // 6

// Rest parameter collects all remaining elements into an array.
function showMovie(title, year, ...actors) {
  console.log(
    `${title} is released in ${year} and in the cast are: ${actors[0]} and ${actors[1]}.`
  );
}

showMovie('Titanic', '1997', 'Leonardo Di Caprio', 'Kate Winslet');