const numbers = [1, 2, 3, 4]
const fruits = ['Apple', 'Banana', 'Cherry']
console.log(numbers[1])
console.log(fruits[2])
const numbers = [1, 2, 3, 4]
const fruits = ['Apple', 'Banana', 'Cherry']
console.log(numbers.length)
console.log(fruits.length)
console.log([1, 2].length)
console.log([].length) //빈 배열, 빈배열의 아이템의갯수 0
const numbers = [1, 2, 3, 4]
const fruits = ['Apple', 'Banana', 'Cherry']
console.log(numbers.concat(fruits)) // [1, 2, 3, 4, "Apple", "Banana", "Cherry"]
console.log(numbers) //(4) [1, 2, 3, 4]
console.log(fruits) //(3) ["Apple", "Banana", "Cherry"]
const numbers = [1, 2, 3, 4]
const fruits = ['Apple', 'Banana', 'Cherry']
fruits.forEach(function (element, index, array) {
console.log(element, index, array)
})
또는
fruits.forEach(function (item, i) {
console.log(item, i)
})
또는
fruits.forEach(function (fruit, i) {
console.log(fruit, i)
})
일반함수 표현
const a = fruits.forEach(function (fruit, index) {
console.log(${fruit}-${index}
)
})
console.log(a) //undefined
화살표함수 표현
const a = fruits.forEach((fruit, index) => {
console.log(${fruit}-${index}
)
})
console.log(a) //undefined
const numbers = [1, 2, 3, 4]
const fruits = ['Apple', 'Banana', 'Cherry']
const b = fruits.map(function (fruit, index) {
return ${fruit}-${index}
//return 키워드를 이용하여 콜백함수 밖으로 반환
})
console.log(b) //["Apple-0", "Banana-1", "Cherry-2"]
일반함수 표현
const b = fruits.map(function (fruit, index) {
return {
id: index,
name: fruit
}
})
console.log(b)
// (3) [{…}, {…}, {…}]
// 0: {id: 0, name: "Apple"}
// 1: {id: 1, name: "Banana"}
// 2: {id: 2, name: "Cherry"}
화살표함수 표현
const b = fruits.map((fruit, index) => ({
id: index,
name: fruit
}))
console.log(b)
// (3) [{…}, {…}, {…}]
// 0: {id: 0, name: "Apple"}
// 1: {id: 1, name: "Banana"}
// 2: {id: 2, name: "Cherry"}