JS 문법 정리 (2)

0. String concatenation

console.log(`string literals :

''''

1+2=${1+2}`);

 

1. Increment and decrement operators

let counter = 2;

const preIncrement = ++counter;

counter = counter + 1;

preIncrement = counter;

const postIncrement = counter++;

postIncrement = counter;

counter = counter + 1;

 

2. Logical operators 

|| or : finds the first truthy value

value1 || value2 || check() // true 는 뒤로!!

 

&& and : finds the first falsy value

if (nullableObject != null) {

nullableObject.something;

}

 

! not : change boolean

 

3. Equality

const stringFive = '5';

const numberFive = 5;

 

loose equality, with type converstion

stringFive == numberFive

stringFive != numberFive

 

strict equality, no type converstion //웬만하면 이거~

stringFive === numberFive

stringFive !== numberFive

 

+ object equality by reference

const a1 = {name : 'a'};

const a2 = {name : 'a'};

const a3 = a1;

console.log(a1 == a2); f //다른 reference 저장

console.log(a1 === a2); f //reference 값 다름

console.log(a1 === a3); t

 

+ quiz

0 == false T

0 === false F

' ' == false T

' ' === false F

null == undefined T

null === undefined F

 

4. Ternary operator : ?

// condition ? value1 : value2

const name = 'b'

console.log(name === 'a' ? 'yes' : 'no');

 

5. Switch

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('a');

  break;

case 'Chrome':

  console.log('b');

  break;

default:

  console.log('c');

  break;

}

 

6. Loops (while/ do/ for)

- while

let i = 3;

while (i>0) {

console.log(`while:${i}`);

i--;

}

 

- do // 블록 실행 후 조건 맞는지 안맞는지 검사. 블록 먼저 실행하고 싶을 때

do {

console.log(`while:${i}`);

i--;

} while (i>0);

 

- for

for (i=3; i>0; i--) { //let i=3 으로 해도 좋음

console.log(`for:${i}`);

}

 

+ nested loops

for (let i=0; i<10; i++) {

for (let i=0; i<10; i++) {

  console.log(`i:${i}, j:${j}`);

}

}

→ O(n**2) 은 CPU에 좋지 않음

 

7.break vs continue

break : 루프 완전 끝냄

continue : 다음 스탭으로 넘어감.

 

+ quiz 

for (let i = 0; i<11; i++){

    if ( i % 2 !== 0 ){

    continue;

    }

console.log(i);

}

for (let a = 0; a<11; a++){

    if (a > 8){

        break;

    }

console.log(a);

}