[JavaScript] 4. 코딩의 기본 operator

 

1. String concatenation

console.log('my' + 'car');
console.log('1' + 2);
console.log(`string literals : 1 + 2 = ${1 + 2}`);

 

2. Numeric operators

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); // exponentiation

 

3. Increment & Decrement operators : ++, --

let a = 2;
const b = ++a; // a === 3, b === 3

let c = 2;
const d = c++; // c === 2, d === 3

 

4. Assignment operators

let x = 3;
let y = 6;
x += y; // x = x + y;
x -= y; // x = x - y;
x *= y; // x = x * y;
x /= y; // x = x / y;

 

5. Comparison operators : <, >, <=, >=

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 : ||, &&

const v1 = false;
const v2 = 4 < 2;

// ||(or), finds the first truthy value
console.log(`or : ${v1 || v2 || check()}`); // v1이 true이면, 뒷연산 없이 바로 true 출력

// &&(and), finds the first falsy value
console.log(`and : ${v1 && v2 && check()}`); // v1이 false이면, 뒷연산 없이 바로 false 출력

function check() { // 그냥 시간을 낭비하는 함수
	for (let i = 0; i < 10; i++) {
    	console.log('*');
    }
    return true;
}

// Not(!)
let v = true;
console.log(!v); // false

often used to compress long if-statement

if (nullableObject && nullableObject.something) {
}

// 두 조건은 같다.

if (nullableObject != null) {
	nullableObject.something;
}

 

7. Equality : ==, ===

const stringFive = '5';
const numberFive = 5;

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

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

const a1 = {name : 'apple'};
const a2 = {name : 'apple'};
const a3 = a1;
console.log(a1 == a2); // false
console.log(a1 === a2); // false
console.log(a1 === a3); // true

console.log(0 == false); // true
console.log(0 === false); // false
console.log('' == false); // true
console.log('' === false); // false
console.log(null == undefined); // true
console.log(null === undefined); // false

 

8. Conditional operators : if, else

const a = 'apple';
if (a === 'banana') {
	console.log('b');
} else if (a === 'grape') {
	console.log('g');
} else {
	console.log('a');
}

 

9. Ternary operator : 삼항연산자

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

 

10. Switch statement : switch, case, break, default

 

11. Loops : while, do, for

let i = 0;
while(i < 3) {
	console.log(`while: ${i}`);
    i++;
}

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

for(i = 0; i < 3; i++) {
	console.log(`for: ${i}`);
}