koyacode

function myFunction() {
  const array1 = [[0, 1], [2, 3], [4, 5]].reduceRight(
//    (accumulator, currentValue) => accumulator.concat(currentValue)
    function(accumulator, currentValue) {return accumulator.concat(currentValue);}
  );
  
  console.log(array1);
  // expected output: Array [4, 5, 2, 3, 0, 1]
}

koyacode

function myFunction() {
  const array1 = [1, 2, 3, 4];
//  const reducer = (accumulator, currentValue) => accumulator + currentValue;
  const reducer = function(accumulator, currentValue) { return accumulator + currentValue;};

  // 1 + 2 + 3 + 4
  console.log(array1.reduce(reducer));
  // expected output: 10
  
  // 5 + 1 + 2 + 3 + 4

koyacode

function myFunction() {
//  var power = function(x) { return x * x;}; // JavaScript 1.7 and older
  var power = function(x) x * x; // error

  var result = power(10);

  console.log(result);
}

koyacode

function destructuringAssignment() {
  var a, b, rest;
  [a, b] = [10, 20];
  
  console.log(a);
  // expected output: 10
  
  console.log(b);
  // expected output: 20
  

koyacode

function constFunction() {
  const number = 42;
  
  try {
    number = 99;
  } catch(err) {
    console.log(err);
    // expected output: TypeError: invalid assignment to const `number'
    // Note - error messages will vary depending on browser
  }

koyacode

function letFunction() {
  let x = 1; // error
  
  if (x === 1) {
    let x = 2; // error
  
    console.log(x);
    // expected output: 2
  }
  

koyacode

function mapFunction() {
  var numbers = [1, 2, 3, 4];

//  var doubled = numbers.map(i => i * 2);
  var doubled = numbers.map(function(i) {return i * 2;});
    
  console.log(doubled); // logs 2,4,6,8
}

function filterFunction() {

koyacode

function myFunction() {
  [for (i of [1, 2, 3]) i * i ]; // error
  // [1, 4, 9]
  
  var abc = ['A', 'B', 'C'];
  [for (letters of abc) letters.toLowerCase()]; // error
  // ["a", "b", "c"]
}

koyacode

function* makeRangeIterator(start, end, step) { // error
    var iterationCount = 0;
    for (var i = start; i < end; i += step) {
        iterationCount++;
        yield i; // error
    }
    return iterationCount;
}

function useMakeRangeIterator() {

koyacode

function makeRangeIterator(start, end, step) {

    var nextIndex = start;
    var iterationCount = 0;

    var rangeIterator = {
       next: function() {
           var result;
           if (nextIndex < end) {
               result = { value: nextIndex, done: false }