[javascript] forEach, map, filter, reduce 함수

forEach

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

a.forEach(function (v, i) {
    console.log(v, i, this);
});

10 0
11 1
12 2
13 3
14 4
15 5

map

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

let answer = a.map(function (v, i) {
    return v * v;
});
console.log(answer);

[100, 121, 144, 169, 196, 225]

filter

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

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

[10, 12, 14]

reduce

배열의 합 구할 때 많이 씀

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

let answer = a.reduce(function (acc, v) {
    return acc + v;
}, 0);
console.log(answer);

75