operator.js

// 1. String concatenation(문자열 + 문자열)
console.log('my' + ' cat')
console.log('1' + 2)
console.log(`string literals: 1+ 2 = ${1 + 2}`)

// 2. Numeric operators(숫자 연산)
console.log(1 + 1) // add
console.log(1 - 1) // substract
console.log(1 / 1) // divide
console.log(1 * 1) // multiply
console.log(5 % 2) // remainder
console.log(2 ** 3) // --> 2^3 exponentiation 

// 3. Increment and decrement operators(증가 감소)
let counter = 2
const preIncrement = ++counter
// counter = counter + 1
// preIncrement = counter
console.log(`preIncrement: ${preIncrement}, counter: ${counter}`)
const postIncrement = counter++
// postIncrement = counter;
// counter = counter + 1
console.log(`preIncrement: ${postIncrement}, counter: ${counter}`)
const preDecrement = --counter
console.log(`preIncrement: ${preDecrement}, counter: ${counter}`)
const postDecrement = counter--
console.log(`preIncrement: ${postDecrement}, counter: ${counter}`)

// 4. Assigment operators(할당)
let x = 3
let y = 6
x += y // x = x + y
x -= y
x *= y
x /=y

// 5. Comparison operators (비교)
console.log(10 < 6) // less than
console.log(10 <= 6) // less than or equal
console.log(10 > 6) // greater than
console.log(10 >=6) // greater than or equal

// 6. Logical operators : || (or), && (and), ! (not)
const value1 = true
const value2 = 4 < 2

// || (or), finds the first truthy value (처음으로 true가 나오면 멈춤)
console.log(`or : ${value1 || value2 || check()}`)

// && (and)), finds the first falsy value (처음으로 false가 나오면 멈춤)
console.log(`and : ${value1 && value2 && check()}`)

// often used to compress long if - statement 
// nullableObject && nullableObject.something (간편한 null 체크할때도 사용)
// if(nullableObject !=null){
//     nullableObject.something
// }

function check(){
    for(let i=0; i<10; i++){
        //wasting time
        console.log('ㅠㅠ')
    }
    return true
}

// ! (not)
console.log(!value1)

// 7. Equality
const stringFive = '5'
const numberFive = 5

// == loose equality, with type conversion
console.log(stringFive == numberFive)
console.log(stringFive != numberFive)

// === strict equality, no type conversion
console.log(stringFive === numberFive)
console.log(stringFive !== numberFive)

// object equality by reference
const ellie1 = { name: 'ellie'}
const ellie2 = { name: 'ellie'}
const ellie3 = ellie1
console.log(ellie1 == ellie2)
console.log(ellie1 === ellie2)
console.log(ellie1 === ellie3)

// equality = puzzler
console.log(0 == false)
console.log(0 === false)
console.log('' == false)
console.log('' === false)
console.log(null == undefined)
console.log(null === undefined)

// 8. Conditional operators : if
// if, else if , else
const name = 'ellie'
if(name==='ellie'){
    console.log('Welcome, Ellie!')
}else if(name==='coder'){
    console.log('You are amazing coder')
}else{
    console.log('unkwnon')
}

// 9. Ternary operator: ?
// condition ? value1 : value2 ;
console.log(name === 'ellie' ? 'yes' : 'no')

// 10. Switch statement
// use for multiple if checks
// use for enum-like value check
// use for multiple type checks in TS
const browser = 'IE'
switch(browser){
    case 'IE' :
        console.log('go away!')
        break;
    case 'Chrome':
    case 'Firefox':
        console.log('love you!')
        break
    default:
        console.log('same all!')
        break
}

// 11. Loops
// while loop, while the condition is truthy,
// body code is executed.
let i = 3
while (i>0){ // statement가 false로 나오기 전까지 무한대로 반복해서 돈다. 
    console.log(`while: ${i}`)
    i--;
}

// do while loop, body code is executed first,
// than check the condition.

do{
    console.log(`do while: ${i}`)
    i--;
} while (i>0)

// for loop, for(begin; condition; step)
for(i = 3; i>0; i--){
    console.log(`for: ${i}`)
}

for (let i=3; i>0; i=i-2){
    // inline variable declaration
    console.log(`inline variable for: ${i}`)
}

// nested loops
for(let i =0; i<10; i++){
    for(let j = 0; j<10; j++){
        console.log(`i: ${i}, j: ${j}`)
    }
}

// break, continue
// Q1. iterate from 0 to 10 and print only even numbers(use continue)

for(let i=0; i<11; i++){
    if(i%2==0){
        console.log(`Q1. ${i}`)
    }
}

for(let i=0; i<11; i++){
    if(i%2 == 1) continue
    console.log(`Q1. ${i}`)
}

// Q2. iterate from 0 to 10 and print numbers nutil reaching 8 (use break)

for (let i =0; i<11; i++){
    if(i>8) break
    console.log(`Q2. ${i}`)
}