Learn Javascript -6 "Loops"

A loop is a programming tool that repeats a set of instructions until a specified condition, called a stopping condition is reached. As a programmer, you’ll find that you rely on loops all the time! You’ll hear the generic term iterate when referring to loops; iterate simply means “to repeat”.
[The For Loop}
The typical for loop includes an 反復変数(反復変数) that usually appears in all three expressions. The iterator variable is initialized, checked against the stopping condition, and assigned a new value on each loop iteration. Iterator variables can have any name, but it’s best practice to use a descriptive variable name.
A for loop contains three expressions separated by ; inside the parentheses:

an initialization starts the loop and can also be used to declare the iterator variable.

a stopping condition is the condition that the iterator variable is evaluated against— if the condition evaluates to true the code block will run, and if it evaluates to false the code will stop.

an iteration statement is used to update the iterator variable on each loop.

for (let counter = 0; counter < 4; counter++) {
  console.log(counter);
}
initialization(초기선언문)

let counter = 0

정지조건은 ```counter < 4```임. 4보다 작을때까지 반복이 됨.

반복문은 ```counter++```. 각 루프에서 1씩 증가하는것을 뜻함. 첫번째에서는 0일테고, 두번째 반복에서는 1, …

{} 안의 코드블럭은 값이 ‘false’일때까지 실행되게 됨.

This for loop makes it possible to write 0, 1, 2, and 3 programmatically.

[Looping in Reverse]
도 응용할 수 있음. 

[Looping through Arrays]
for loops are very handy for iterating over data structures.
반복적인 데이터 구조에서 매우 유용한 ```for```루프.
array의 각각의 요소에 반복적인 operation을 작동시킬때 사용할 수 있습니다. array는 ‘고객이름’, ‘제품정보’같은 데이터 리스트’를 나타냅니다.

array의 각 요소를 반복하려면 for 루프가 해당 조건에서 배열의 .length 속성을 사용해야합니다.

const animals = ['Grizzly Bear', 'Sloth', 'Sea Lion'];
for (let i = 0; i < animals.length; i++){
console.log(animals[i]);
}

Grizzly Bear
Sloth
Sea Lion

I(index의 약자).
중지 조건이 i가 animals.length보다 작을때임. 
Remember that arrays are zero-indexed, the index of the last element of an array is equivalent to the length of that array minus 1. 

const vacationSpots = ['Bali', 'Paris', 'Tulum'];
//Write your code below
for (let i = 0; i < vacationSpots.length; i++){
console.log('I would love to visit ' + vacationSpots[i])
}