javaScript 문법 forEach, map, filter

1. forEach

for문처럼 사용하기 위한 문법

const a = [10, 11, 12, 13, 14, 15];

a.forEach((a, i, arr) => {
  console.log(a * a, i, arr);
});

100 0 [ 10, 11, 12, 13, 14, 15 ]
121 1 [ 10, 11, 12, 13, 14, 15 ]
144 2 [ 10, 11, 12, 13, 14, 15 ]
169 3 [ 10, 11, 12, 13, 14, 15 ]
196 4 [ 10, 11, 12, 13, 14, 15 ]
225 5 [ 10, 11, 12, 13, 14, 15 ]

 

 

2. map

새로운 배열로 만들며 값이 반환된다

const a = [10, 11, 12, 13, 14, 15];

let answerMap = a.map((a, i) => {
  return a * i;
});
console.log(answerMap) 

[ 0, 11, 24, 39, 56, 75 ]

 

3.filter

해당되는 값만 뽑아서 보여준다

const a = [10, 11, 12, 13, 14, 15];

let answerFilter = a.filter((v, i) => {
  return v % 2 === 0;
});
console.log(answerFilter);

[ 10, 12, 14 ]