🌚 Replit

array.map()

// Convert string into number
function solution(element, index, array) {
		return Number(element)
}

// Convert the last string into number
function solution(element, index, array) {
	if (index === array.length-1){
      element = Number(element)
    }
 return element
}

const arr = ['1', '2', '3'];
const result = arr.map(solution);
console.log(result); // [1, 2, 3]

String Detection Method

const email = '[email protected]'; 

console.log(email.startsWith('pre'));   //true
console.log(email.endsWith('com'));     //true
console.log(email.includes('@gmail'));  //true
console.log(email.endsWith('@gmail.com'));  //true

🌝 Class

padStart

let str = ""
str.padStart(5, 'z')	// 'zzzzz'

str.padStart(5, "*") // '*****'

slice

// 1. 배열, 문자열을 자를 때 사용
// 2. 원본이 저장되지 않음

str = "abcde"
str.slice(2)

🍃 Ternary Operator

// 삼항 연산자 사용
function solution(num){
    return num % 2 === 0? "Even" : "Odd"
}

🍃 Masking phone number

function solution(phone_number){
    let answer = ''
    
    for (let i = 0; i<phone_number.length; i++){
        if (i< phone_number.length -4){
            answer += '*'
        }
        else {
            answer += phone_number[i]
        }
    }
    return answer
}

// => refactoring
function solution(phone_number){
    let answer = ''
    
    answer = answer.padStart(phone_number-4, "*")
    answer += phone_number.slice(phone_number.length -4, phone_number.length)
    return answer
}

🍃 reduce() method

// ======== 평균값 구하기 ========
function solution(arr){
    //reduce = for loop 
    // 계속 반복하는건데 reduce는 acc(누적값)이라는거 자체가 이전 값을 계속 받아오는거임
      const sum = arr.reduce( (acc, cur) => {
          console.log(acc, cur)	// acc = 누적값 // cur = 현재 값
            return acc + cur
      },0)
      return sum/arr.length
  }