csbin-callbacks.js

// From http://csbin.io/callbacks
// Video: https://www.youtube.com/watch?v=py8gaw6DXRM
// Slides: https://drive.google.com/file/d/0B44cfJmZKU0hQnRIRkpzNi1CWW8/view

// Type JavaScript here and click "Run Code" or press Ctrl + s
console.log('Hello, world!');


// Challenge 1
function addTwo(num) {
	return num + 2;
}

// To check if you've completed it, uncomment these console.logs!
// console.log(addTwo(3));
// console.log(addTwo(10));


// Challenge 2
function addS(word) {
	return word + 's';
}

// uncomment these to check your work
// console.log(addS('pizza'));
// console.log(addS('bagel'));


// Challenge 3
function map(array, callback) {
	var result = [];
  
  for (var i = 0; i < array.length; i++) {
    result.push(callback(array[i]));
  }
  
  return result;
}

// console.log(map([1, 2, 3], addTwo));


// Challenge 4
function forEach(array, callback) {
	for (var i = 0; i < array.length; i++) {
    callback(array[i]);
  }
}

// see for yourself if your forEach works!
// var alphabet = '';
// var letters = ['a', 'b', 'c', 'd'];
// forEach(letters, function(char) {
//   alphabet += char;
// });
// console.log(alphabet);


//--------------------------------------------------
// Extension
//--------------------------------------------------

//Extension 1
function mapWith(array, callback) {
	var result = [];
  
  forEach(array, function(item) {
    result.push(callback(item));
  });
  
  return result;
}

// console.log(mapWith([1, 2, 3], addTwo));

//Extension 2
function reduce(array, callback, initialValue) {
	var result = initialValue;
  
  forEach(array, function(item) {
    result = callback(result, item);
  });
  
  return result;
}

// var nums = [4, 1, 3];
// var add = function(a, b) { return a + b; }
// console.log(reduce(nums, add, 0));

//Extension 3
function intersection(arrays) {
  var arrays = (arguments.length === 1 ? [arguments[0]] : Array.apply(null, arguments));

  if (arrays.length <= 1) return [];

  return reduce(arrays.slice(1, arrays.length), function(arr1, arr2) {
    var result = [];

    for (var i = 0; i < arr2.length; i++) {
      if (arr1.indexOf(arr2[i]) >= 0) {
        result.push(arr2[i]);
      }
    }
    
    return result;
  }, arrays[0]);
}

// console.log(intersection([5, 10, 15, 20], [15, 88, 1, 5, 7], [1, 10, 15, 5, 20]));
// should log: [15, 5]

//Extension 4
function union(arrays) {
	var arrays = (arguments.length === 1 ? [arguments[0]] : Array.apply(null, arguments));
  
  if (arrays.length === 0) return [];
  if (arrays.length === 1) return arrays[0];
  
  return reduce(arrays.slice(1, arrays.length), function(arr1, arr2) {
    var result = arr1.slice();
    
    for (var i = 0; i < arr2.length; i++) {
      if (result.indexOf(arr2[i]) === -1) {
        result.push(arr2[i]);
      }
    }
    
    return result;
  }, arrays[0]);
}

// console.log(union([5, 10, 15], [15, 88, 1, 5, 7], [100, 15, 10, 1, 5]));
// should log: [5, 10, 15, 88, 1, 7, 100]