Traversing arrays and objects in CoffeeScript

ArrayObjectDemo.coffee

# Traversing arrays and objects in CoffeeScript

# The array and object we use for testing
arr = [1, 2, 3, 4, 5]
obj = {a: 1, b: 2, c: 3, d: 4, e: 5}


# 'in' has a different meaning in CoffeeScript than in JavaScript
# CS: element in array -> JS: array.indexOf(element) >= 0
console.log '5 in arr: ' + (5 in arr)
console.log '5 in obj: ' + (5 in obj)
console.log 'e in obj: ' + ('e' in obj)

# 'of' in CoffeeScript is the 'in' known in JavaScript
# CS: key of object -> JS: key in object
console.log '5 of arr: ' + (5 of arr)
console.log '5 of obj: ' + (5 of obj)
console.log 'e of obj: ' + ('e' of obj)

# Traverse through an array
# CS: for i in arr -> JS: for( var i; i < arr.length; i++ )
# CS: i -> JS: arr[i]
console.log 'i in arr'
for i in arr
	console.log i

# CS: i -> JS: i, where i is an index 
# This will return only results for keys that 
# are numbers and within the range of the index
console.log 'i in obj'
for i in obj
	console.log i

# CS: for i of arr -> JS for( i in arr )
# CS: i -> JS: i, where i is an object key
# Basically, the same as JS: for( i in Object.keys(arr) )
console.log 'i of arr'
for i of arr
	console.log i

# This is the CS version of JS' for( k in obj )
console.log 'k of obj'
for k of obj
	console.log k

# CS: k, v -> JS: k, obj[k]
console.log 'k, v of obj'
for k, v of obj
	console.log k + ': ' + v

# array.forEach is a method and thus behaves consistently
# https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/forEach
console.log 'array.forEach(callback(v, k, arr))'
arr.forEach (element, index, array) ->
	if index == 0
		console.log 'arr == array: ' + (arr == array)
	console.log index + ': ' + element

# .forEach is only available for arrays, not for objects

ArrayObjectDemo.js

(function() {
  var arr, i, k, obj, v, _i, _j, _len, _len2,
    __indexOf = Array.prototype.indexOf || function(item) { for (var i = 0, l = this.length; i < l; i++) { if (i in this && this[i] === item) return i; } return -1; };

  arr = [1, 2, 3, 4, 5];

  obj = {
    a: 1,
    b: 2,
    c: 3,
    d: 4,
    e: 5
  };

  console.log('5 in arr: ' + (__indexOf.call(arr, 5) >= 0));

  console.log('5 in obj: ' + (__indexOf.call(obj, 5) >= 0));

  console.log('e in obj: ' + (__indexOf.call(obj, 'e') >= 0));

  console.log('5 of arr: ' + (5 in arr));

  console.log('5 of obj: ' + (5 in obj));

  console.log('e of obj: ' + ('e' in obj));

  console.log('i in arr');

  for (_i = 0, _len = arr.length; _i < _len; _i++) {
    i = arr[_i];
    console.log(i);
  }

  console.log('i in obj');

  for (_j = 0, _len2 = obj.length; _j < _len2; _j++) {
    i = obj[_j];
    console.log(i);
  }

  console.log('i of arr');

  for (i in arr) {
    console.log(i);
  }

  console.log('k of obj');

  for (k in obj) {
    console.log(k);
  }

  console.log('k, v of obj');

  for (k in obj) {
    v = obj[k];
    console.log(k + ': ' + v);
  }

  console.log('array.forEach(callback(v, k, arr))');

  arr.forEach(function(element, index, array) {
    if (index === 0) console.log('arr == array: ' + (arr === array));
    return console.log(index + ': ' + element);
  });

}).call(this);