14-ES6ParameterHandling.js

// @ts-check

//* ****** EcmaScript 6: Default Parameter Values
function sum(x = 1, y = 2, z = 3) {
  return x + y + z;
}
console.log(sum(4, 2)); // outpus 9

// function above is the same as
function sum2(x, y, z) {
  if (x === undefined) x = 1;
  if (y === undefined) y = 2;
  if (z === undefined) z = 3;
  return x + y + z;
}
console.log(sum2(4, 2)); // outpus 10

//* ****** EcmaScript 6: spread operator ('...')
var params = [3, 4, 5];
console.log(sum(...params));

var numbers = [1, 2, ...params]; // pushing values into array
console.log(numbers);

//* ****** EcmaScript 6: rest parameter ('...')
function restParamaterFunction(x, y, ...a) {
  return (x + y) * a.length;
}
console.log(restParamaterFunction(1, 2, 'hello', true, 7)); // outputs 9;

// code above is the same as ES5:
function restParamaterFunction2(x, y) {
  var a = Array.prototype.slice.call(arguments, 2);
  return (x + y) * a.length;
}
console.log(restParamaterFunction2(1, 2, 'hello', true, 7));