자바스크립트 연산자 반복문 11가지(feat. 드림코딩 앨리님♡)

출처

//1. String concatenation

console.log('my' + ' cat');

console.log('1' + 2); // 문자화된 숫자에 숫자를 더하면 숫자가 문자화 되어 12로 표현됨.

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

console.log("nice to \n \t meet you"); // \n 줄바꿈 \t 탭

// 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); // remiander

console.log(2 ** 3); // exponentiation 제곱

// 3 .Increment and decrement operators

let counter = 2;

const preIncrement = ++counter;

// counter = counter + 1; counter 에 1을 더한 것을 counter에 할당

// preIncrement = counter; counter를 preIncrement에 할당

console.log(counter); console.log(preIncrement);

const postIncremnet = counter++;

//postIncrement = counter;

//counter = counter + 1;

console.log(postIncremnet);

console.log(counter);

const preDecrement = --counter;

//counter = counter - 1;

//preDecrement = counter

console.log(`preDecrement: ${preDecrement}, counter: ${counter}`);

const postDecrement = counter--;

//postDecrement = counter;

//counter = counter - 1;

console.log(`postDecrement: ${postDecrement}, counter: ${counter}`);

// 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

 

 

 

집중!!

//6. Logical operators: || (or), && (and), ! (not)

// 연산을 많이하는 함수 or expression들 앞에두지 말 것. 심플한것들 앞에 배치

const value1 = true;

const value2 = 4 < 2;

// || (or) finds the first truthy value 하나라도 참이라면 true , true 발견하면 뒤에값 계산 안함

console.log(`or: ${value1 || value2 || check()}`);

// &&(and), finds the first falsy value 하나라도 false면 false

console.log(`and: ${value1 && value2 && check()}`);

//often used to compress long if-statement

//nullableObject && nullableObject.something

//  if (nullableObject != null) {

//     nullableObject.something;

// }

function chenk() {

    for (let i = 0; i < 10; i++) {

        //wasting time

        console.log('^^!')

    }

    return true;

}

// ! (not)

console.log(!value1);

// 7. Equality

const stringFive = '5';

const numberFive = 5;

// == losse 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); // ture

//object equality by reference

const ellie1 = {name: 'ellie'};

const ellie2 = {name: 'ellie'};

const ellie3 = ellie1;

console.log(ellie1 == ellie2);  // false

console.log(ellie1 === ellie2); // false

console.log(ellie1 === ellie3); // true

// 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('unknown');

}

// 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) {

    console.log(`while: ${i}`);

    i--;

}

// do while loop, body code is excuted first,

// then 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. literate from 0 to 10 and print only even nembers (use continue)

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

let k = 0;

while (k <= 10) {

    k += 1;

    if ((k % 2) == 1)

        continue;

     console.log(k);

}

let h = 0;

while (h <= 10) {

    console.log(h);

    h += 1;

    if (h > 8)

    break;

}

//답

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

    if ((i % 2) !== 0) {

    continue;

    }

    console.log(i);

}

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

    if(i > 8) {

        break;

    }

    console.log(i);

}