Question

What is a rest parameter?

Answer 1

Rest parameter is an improved way to handle function parameters which allows us to represent an indefinite number of arguments as an array. The syntax would be as below,

function f(a, b, ...theArgs) {
  // ...
}

For example, let's take a sum example to calculate on dynamic number of parameters,

function sum(...args) {
  let total = 0;
  for (const i of args) {
    total += i;
  }
  return total;
}

console.log(sum(1, 2)); //3
console.log(sum(1, 2, 3)); //6
console.log(sum(1, 2, 3, 4)); //13
console.log(sum(1, 2, 3, 4, 5)); //15

Note: Rest parameter is added in ES2015 or ES6