Gist on understanding closures - Javascript

closure.js

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

// CHALLENGE 1
function createFunction() {
	return function(){
    console.log('hello');
  }
}

// /*** Uncomment these to check your work! ***/
const function1 = createFunction();
function1(); // => should console.log('hello');


// CHALLENGE 2
function createFunctionPrinter(input) {
		return function(){
      console.log(input);
    }
}

// /*** Uncomment these to check your work! ***/
const printSample = createFunctionPrinter('sample');
printSample(); // => should console.log('sample');
const printHello = createFunctionPrinter('hello');
printHello(); // => should console.log('hello');


// CHALLENGE 3
function outer() {
  let counter = 0; // this variable is outside incrementCounter's scope
  function incrementCounter () {
    counter ++;
    console.log('counter', counter);
  }
  return incrementCounter;
}

const willCounter = outer();
const jasCounter = outer();

// Uncomment each of these lines one by one.
// Before your do, guess what will be logged from each function call.

// /*** Uncomment these to check your work! ***/
willCounter();  // 1
willCounter();  // 2
willCounter();  // 3

jasCounter();   // 1
willCounter();  // 4


function addByX(x) {
	return function(y){
    return x+y;
  }
}

// /*** Uncomment these to check your work! ***/
const addByTwo = addByX(2);
addByTwo(1); // => should return 3
addByTwo(2); // => should return 4
addByTwo(3); // => should return 5

const addByThree = addByX(3);
addByThree(1); // => should return 4
addByThree(2); // => should return 5

const addByFour = addByX(4);
addByFour(4); // => should return 8
addByFour(5); // => should return 9


// CHALLENGE 4
function once(func) {
	var counter = 0;
  var output = 0;
  return function(num){
    if (counter == 0){
      counter++;
      output = func(num)
    }
    return output;
  }
}

// /*** Uncomment these to check your work! ***/
const onceFunc = once(addByTwo);
console.log(onceFunc(4));  // => should log 6
console.log(onceFunc(10));  // => should log 6
console.log(onceFunc(9001));  // => should log 6


// CHALLENGE 5
function after(count, func) {
	var counter = 1;
  return function(){
    if (counter >= count){
      func()
    }
    else{
      counter++;
    }
  }
}

// /*** Uncomment these to check your work! ***/
console.log('------------------');
const called = function() { console.log('hello') };
const afterCalled = after(3, called);
afterCalled(); // => nothing is printed
afterCalled(); // => nothing is printed
afterCalled(); // => 'hello' is printed


// CHALLENGE 6
function delay(func, wait) {
	setTimeout(func(),wait);
}


// CHALLENGE 7
function rollCall(names) {
	var count = 0;
  return function (){
    if (count < names.length){
      console.log(names[count]);
      count++
    }
    else{
      console.log("Everyone account for")
    }
  }
}

// /*** Uncomment these to check your work! ***/
const rollCaller = rollCall(['Victoria', 'Juan', 'Ruth'])
rollCaller() // => should log 'Victoria'
rollCaller() // => should log 'Juan'
rollCaller() // => should log 'Ruth'
rollCaller() // => should log 'Everyone accounted for'


// CHALLENGE 8
function saveOutput(func, magicWord) {
	var obj = {};
  var output;
  return function(arg){
    if (arg != magicWord){
			output = func(arg);
    	obj[arg] = output;
      return output;
    }
    else{
    	return obj; 
    }
  }
}

// /*** Uncomment these to check your work! ***/
const multiplyBy2 = function(num) { return num * 2; };
const multBy2AndLog = saveOutput(multiplyBy2, 'boo');
console.log(multBy2AndLog(2)); // => should log 4
console.log(multBy2AndLog(9)); // => should log 18
console.log(multBy2AndLog('boo')); // => should log { 2: 4, 9: 18 }


// CHALLENGE 9
function cycleIterator(array) {
  var count = -1;
  return function(){
    if (count+1 < array.length){
      count++;
      return array[count]
    }
    else{
      count = 0;
      return array[count];
    }
  }

}

// /*** Uncomment these to check your work! ***/
const threeDayWeekend = ['Fri', 'Sat', 'Sun'];
const getDay = cycleIterator(threeDayWeekend);
console.log(getDay()); // => should log 'Fri'
console.log(getDay()); // => should log 'Sat'
console.log(getDay()); // => should log 'Sun'
console.log(getDay()); // => should log 'Fri'


// CHALLENGE 10
function defineFirstArg(func, arg) {
	return function(second){
    return func(arg,second);
  }
}

// /*** Uncomment these to check your work! ***/
const subtract = function(big, small) { return big - small; };
const subFrom20 = defineFirstArg(subtract, 20);
console.log(subFrom20(5)); // => should log 15


// CHALLENGE 11
function dateStamp(func) {
	return function(){
    var today = new Date();
    today = today.getFullYear()+'-'+(today.getMonth()+1)+'-'+today.getDate();
    return {
      date: today,
      output: func(arguments[0])
    }
  }
}

// /*** Uncomment these to check your work! ***/
const stampedMultBy2 = dateStamp(n => n * 2);
console.log(stampedMultBy2(4)); // => should log { date: (today's date), output: 8 }
console.log(stampedMultBy2(6)); // => should log { date: (today's date), output: 12 }


// CHALLENGE 12
function censor() {
	var d = {}
  
  return function(first,second=null){
    if (second != null){
      d[first] = second
      console.log(d);
    }
    else{
      for(let key in d){
        first = first.replace(key,d[key])
      }
      return first
    }
  }
}

// /*** Uncomment these to check your work! ***/
const changeScene = censor();
changeScene('dogs', 'cats');
changeScene('quick', 'slow');
console.log(changeScene('The quick, brown fox jumps over the lazy dogs.')); // => should log 'The slow, brown fox jumps over the lazy cats.'


// CHALLENGE 13
function createSecretHolder(secret) {
	let mysecret = secret;
  return {
    getSecret: () => console.log(mysecret),
    setSecret: (value) => mysecret = value
  }
}

// /*** Uncomment these to check your work! ***/
let obj = createSecretHolder(5)
obj.getSecret() // => returns 5
obj.setSecret(2)
obj.getSecret() // => returns 2


// CHALLENGE 14
function callTimes() {
	var count = 1;
  return function(){
    return console.log(count++);
  }
}

// /*** Uncomment these to check your work! ***/
let myNewFunc1 = callTimes();
let myNewFunc2 = callTimes();
myNewFunc1(); // => 1
myNewFunc1(); // => 2
myNewFunc2(); // => 1
myNewFunc2(); // => 2


// CHALLENGE 15
function russianRoulette(num) {
	var count = 0;
  
  return function(){
    count++;
    if (count < num){
      return 'click';
    }
    else if (count == num){
      return 'bang';
    }
    else{
      return 'reload to play again'
    }
  }
}

// /*** Uncomment these to check your work! ***/
const play = russianRoulette(3);
console.log(play()); // => should log 'click'
console.log(play()); // => should log 'click'
console.log(play()); // => should log 'bang'
console.log(play()); // => should log 'reload to play again'
console.log(play()); // => should log 'reload to play again'


// CHALLENGE 16
function average() {
  var average = 0;
  var count = 0;
  
  return function(num=null){
    if (num != null){
      let total = (average*count) + num;
      count++;
      average = total/count;
    }
    return average;
  }

}

// /*** Uncomment these to check your work! ***/
const avgSoFar = average();
console.log(avgSoFar()); // => should log 0
console.log(avgSoFar(4)); // => should log 4
console.log(avgSoFar(8)); // => should log 6
console.log(avgSoFar()); // => should log 6
console.log(avgSoFar(12)); // => should log 8
console.log(avgSoFar()); // => should log 8


// CHALLENGE 17
function makeFuncTester(arrOfTests) {
  var array = [...arrOfTests];
  
  return function(callback){
    return array.every((value) => value[1] == callback(value[0]))
  }
}

// /*** Uncomment these to check your work! ***/
const capLastTestCases = [];
capLastTestCases.push(['hello', 'hellO']);
capLastTestCases.push(['goodbye', 'goodbyE']);
capLastTestCases.push(['howdy', 'howdY']);
const shouldCapitalizeLast = makeFuncTester(capLastTestCases);
const capLastAttempt1 = str => str.toUpperCase();
const capLastAttempt2 = str => str.slice(0, -1) + str.slice(-1).toUpperCase();
console.log(shouldCapitalizeLast(capLastAttempt1)); // => should log false
console.log(shouldCapitalizeLast(capLastAttempt2)); // => should log true


// CHALLENGE 18
function makeHistory(limit) {
	var storage = []
  
  return function(value){
    if (value == 'undo'){
      if (storage.length == 0){
        return 'nothing to undo';
      }
      else{
        return storage.pop() + ' undone';
      }
    }
    else{
      storage.push(value)
      if (storage.length > limit){
        storage.shift();
      }
      return value + ' done';
    }
  }
}

// /*** Uncomment these to check your work! ***/
const myActions = makeHistory(2);
console.log(myActions('jump')); // => should log 'jump done'
console.log(myActions('undo')); // => should log 'jump undone'
console.log(myActions('walk')); // => should log 'walk done'
console.log(myActions('code')); // => should log 'code done'
console.log(myActions('pose')); // => should log 'pose done'
console.log(myActions('undo')); // => should log 'pose undone'
console.log(myActions('undo')); // => should log 'code undone'
console.log(myActions('undo')); // => should log 'nothing to undo'


// CHALLENGE 19
function blackjack(array) {
  var index = 0;
	return function(num1,num2){
    var count = 0;
    var currentTotal = 0;
    return function(){
      if (count == 0){
        count++;
        currentTotal = num1+num2;
        return num1 + num2;
      }
      else if(currentTotal > 21){
        return 'you are done!';
      }
      else{
        currentTotal+=array[index]
        index++;
        
        if (currentTotal > 21){
          return 'bust';
        }
        else{
          return currentTotal;
        }
      }
        
    }
  }
}

// /*** Uncomment these to check your work! ***/

/*** DEALER ***/
const deal = blackjack([2, 6, 1, 7, 11, 4, 6, 3, 9, 8, 9, 3, 10, 4, 5, 3, 7, 4, 9, 6, 10, 11]);

/*** PLAYER 1 ***/
const i_like_to_live_dangerously = deal(4, 5);
console.log(i_like_to_live_dangerously()); // => should log 9
console.log(i_like_to_live_dangerously()); // => should log 11
console.log(i_like_to_live_dangerously()); // => should log 17
console.log(i_like_to_live_dangerously()); // => should log 18
console.log(i_like_to_live_dangerously()); // => should log 'bust'
console.log(i_like_to_live_dangerously()); // => should log 'you are done!'
console.log(i_like_to_live_dangerously()); // => should log 'you are done!'

// /*** BELOW LINES ARE FOR THE BONUS ***/

// /*** PLAYER 2 ***/
const i_TOO_like_to_live_dangerously = deal(2, 2);
console.log(i_TOO_like_to_live_dangerously()); // => should log 4
console.log(i_TOO_like_to_live_dangerously()); // => should log 15
console.log(i_TOO_like_to_live_dangerously()); // => should log 19
console.log(i_TOO_like_to_live_dangerously()); // => should log 'bust'
console.log(i_TOO_like_to_live_dangerously()); // => should log 'you are done!
console.log(i_TOO_like_to_live_dangerously()); // => should log 'you are done!

// // /*** PLAYER 3 ***/
const i_ALSO_like_to_live_dangerously = deal(3, 7);
console.log(i_ALSO_like_to_live_dangerously()); // => should log 10
console.log(i_ALSO_like_to_live_dangerously()); // => should log 13
console.log(i_ALSO_like_to_live_dangerously()); // => should log 'bust'
console.log(i_ALSO_like_to_live_dangerously()); // => should log 'you are done!
console.log(i_ALSO_like_to_live_dangerously()); // => should log 'you are done!