[JS] operator, if, for loop 코드리뷰 팁

Operator

[String concatenation]

- 기본적으로 ', "를 사용

- `을 사용해서 string literals를 생성가능, 줄바꿈이나 특수문자를 사용해도 문자열로 만들어짐

-  특수기호를 출력할때는 \를 앞에 붙여줘야한다.

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

 

[Numeric operators]

// 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

 

[++ -- operators]

// 3. Increment and decrement operators
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(`postIncrement: ${postIncrement}, counter: ${counter}`);
const preDecrement = --counter;
console.log(`preDecrement: ${preDecrement}, counter: ${counter}`);
const postDecrement = counter--;
console.log(`postDecrement: ${postDecrement}, counter: ${counter}`);

 

[= operators]

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

 

[<= operators]

// 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

 

[Logical operators ( ||, &&, ! )]

- or연산자에서 첫번째로 검사한것이 true면 뒤에꺼는 판단하지 않고 끝냄. and 또한 같음

- check()와 같은 무거운 함수를 호출할때 맨앞에 두게 되면 --> 코드 지적질당함 따라서 가벼운것들을 앞에 배치

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

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

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

// often used to compress long if-statement
// nullableObject && nullableObject.something

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

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

 

[Equality operators ( ==, === )]

===은 타입도 평가한다.

// 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); // false
console.log(ellie1 === ellie2); //false
console.log(ellie1 === ellie3); //true

// equality - puzzler
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

 

[Conditional operators : if]

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

 

[Ternary operators]

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

 

[Switch operators

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

 

 

Loop

[while]

// 11. Loops
// while loop, while the condition is truthy,
// body code is executed.
let i = 3;
while (i > 0) {
  console.log(`while: ${i}`); // 3 2 1
  i--;
}

 

[do-while]

// do while loop, body code is executed first,
// then check the condition.
do {
  console.log(`do while: ${i}`); //0
  i--;
} while (i > 0);

 

[for]

// 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 loop]

되도록 중첩 loop는 피하기

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

 

[break, continue]

// 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) {
    continue;
  }
  console.log(`q1. ${i}`);
}

// Q2. iterate from 0 to 10 and print numbers until reaching 8 (use break)
for (let i = 0; i < 11; i++) {
  if (i > 8) {
    break;
  }
  console.log(`q2. ${i}`);
}

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Thanks for 드림코딩

https://youtu.be/YBjufjBaxHo