filter 메서드

filter(callback: (value: T, index?: number): boolean ): T[]

예시

const array: number[] = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]

let odds: number[] = array.filter((value) => value % 2 != 0)
let evens: number[] = array.filter((value) => value % 2 == 0)
console.log(odds, evens) // [ 1, 3, 5, 7, 9 ] [2, 4, 6, 8, 10 ]

map 메서드

map(callback: (value: T, index?: number): Q): Q[]

예시

const names: number[] = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]
	.map((val, index) => `[${index}]: ${val}`)
console.log(names) // [ '[0]: 1', '[1]: 2', '[2]: 3', '[3]: 4', '[4]: 5' ]

reduce 메서드

reduce(callback: (result: T, value: T), initialValue: T):T

예시

const reduceSum: number[] = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]
.reduce((result: number, value: number) => result + value, 0)
console.log(reduceSum) // 5050