JavaScript Loops

루프 : 지정된 조건까지 일련의 지시를 반복하는 프로그래밍 도구

<For Loop>
  for (let counter = 0; counter < 4; counter++) {
   console.log(counter);
  } // Output: 
       0
       1
       2
       3                              
  1. 초기화 루프를 시작하며 반복자 변수 선언
  2. 정지조건은 반복자 변수가 평가되는 조건-
     true로 평가되면 코드실행, false이면 정지
  3. 반복문은 각 루프에서 반복자 변수를 업데이트하는데 사용됨
                    
<Reverse Loop>
 1. 반복기 변수를 초기화 식에서 가장 높은 값으로 설정
 2. 반복기 변수가 원하는 양보다 작을 때 중지 조건 설정
 3. 반복기는 각 반복 후 간격이 감소해야 함
  for (let counter = 3; counter >= 0; counter--){
  console.log(counter);
  } // Output: 
        3
        2
        1
        0

<Array Loop>
  const animals = ['Grizzly Bear', 'Sloth', 'Sea 
   Lion'];
  for (let i = 0; i < animals.length; i++){
   console.log(animals[i]);
  } // Output:
       Grizzly Bear
       Sloth
       Sea Lion   
  다른 예
  const vacationSpots = ['Bali', 'Paris',
  'Tulum'];

  for (let i = 0; i < vacationSpots.length; i++){
   console.log('I would love to visit ' +  
   vacationSpots[i]);
  } // Output: 
      I would love to visit Bali
      I would love to visit Paris
      I would love to visit Tulum
  
<중첩 Loop>
 const myArray = [6, 19, 20];
 const yourArray = [19, 81, 2];
 for (let i = 0; i < myArray.length; i++) {
   for (let j = 0; j < yourArray.length; j++) {
    if (myArray[i] === yourArray[j]) {
      console.log('Both loops have the number: ' +
      yourArray[j])
    }
   }
 };
  다른 예
  let bobsFollowers = ['Joey', 'Monica', 'Ross', 
  'Maria'];
  let tinasFollowers = ['Cherry', 'Monica',  
  'Ross'];
  let mutualFollowers = [];

for (let i = 0; i < bobsFollowers.length; i++){
 for (let j = 0; j < tinasFollowers.length; j++){
    if (bobsFollowers[i] === tinasFollowers[j])
    {
      mutualFollowers.push(bobsFollowers[i]);
    }
   }
  };

<While Loop>
 // A for loop that prints 1, 2, and 3
for (let counterOne = 1; counterOne < 4; counterOne++){
  console.log(counterOne);
}
 
// A while loop that prints 1, 2, and 3
let counterTwo = 1;
while (counterTwo < 4) {
  console.log(counterTwo);
  counterTwo++;
}
  다른 예
  const cards = ['diamond', 'spade', 'heart', 
  'club'];

 let currentCard;
  while (currentCard !== 'spade'){currentCard = cards[Math.floor(Math.random() * 4)]; 
   console.log(currentCard);
 } 
  
<Do...While>
 let countString = '';
 let i = 0;
 
 do {
   countString = countString + i;
   i++;
 } while (i < 5);
 
 console.log(countString);
 다른 예
const firstMessage = 'I will print!';
const secondMessage = 'I will not print!'; 
 
// A do while with a stopping condition that evaluates to false
do {
 console.log(firstMessage)
} while (true === false);
 
// A while loop with a stopping condition that evaluates to false
while (true === false){
  console.log(secondMessage)
};
 다른 예
 let cupsOfSugarNeeded = 4;
 let cupsAdded = 0;

 do{
   cupsAdded++
  console.log(cupsAdded + ' cup was added') 
 }while (cupsAdded< cupsOfSugarNeeded);
 // Output: 
  1 cup was added
  2 cup was added
  3 cup was added
  4 cup was added

<break>
  for (let i = 0; i < 99; i++) {
   if (i > 2 ) {
     break;
   }
  console.log('Banana.');
 }
 
 console.log('Orange you glad I broke out the  
 loop!'); 
  // Output:
     Banana.
     Banana.
     Banana.
     Orange you glad I broke out the loop!
  다른 예
  const rapperArray = ["Lil' Kim", "Jay-Z", 
  "Notorious B.I.G.", "Tupac"];
 for (let i = 0; i < rapperArray.length; i++){
  console.log(rapperArray[i]);
  if (rapperArray[i] === 'Notorious B.I.G.'){
    break;
   }
 }

 console.log("And if you don't know, now you  know.");
 // Output:
    Lil' Kim
    Jay-Z
    Notorious B.I.G.
    And if you don't know, now you know.