코딩의 기본 operator, if, for loop, 코드리뷰 팁

ex)

//1. String concatenation
console.log('my' + 'cat');
console.log('1' + 2);
console.log(`string literals:

''''
1+1`);

console.log("han's \n\tbook");

 

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ex)

//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 and decrement operators
let counter = 2;
const preIncrement = ++counter;
//counter = counter + 1;
//preIncrement = counter;
console.log(`preIncrement: ${preIncrement}, counter: ${counter}`);

 

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ex)

//4.Assignment operators
let x = 3;
let y = 6;
x += y; // x = x + y;
x -= y;
x *= y;
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

 

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ex)

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

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

function check(){
    for(let i = 0; i < 10; i++){
        //wasting time
        console.log('1');
    }
    return true;
}

 

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value1이 true면 check()는 호출되지 않는다. 그러므로 무거운 연산자, 함수일수록 뒤에 두는 것이 좋다.

 

ex)

//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 han1 = {name: 'han'};
const han2 = {name: 'han'};
const han3 = han1;
console.log(han1 == han2);
console.log(han1 === han2);
console.log(han1 === han3);

 

예제 실행 화면

 

ex)

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

 

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ex)

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

//9. Ternary operator: ?
//condition ? value1 : value2;
console.log(name === 'han' ? 'han' : 'jin');

 

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ex)

//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':
        console.log('love you!');
        break;
    case 'Firefox':
        console.log('love you!');
        break;
    default:
        console.log('same all!');
        break;
}

 

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ex)

//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 executed 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){
    console.log(`inline variable for: ${i}`);
}

 

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ex)

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

//break, continue

 

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