배열

배열

배열은 여러개의 데이터를 순차적으로 저장하는 저장소입니다.

var 변수명 = [/*값1, 값2,값3*/]

배열 선언

let arr1 = new Array();
arr1[0] = 100;
arr1[1] = 200;

document.write(arr1[0], "<br />");
document.write(arr1[1]), "<br />");

//100
//200

배열을 선언과 동시에 초기화

let arr2 =  new Array(100, 200, 300);

document.write(arr2[0], "<br>");
document.write(arr2[1], "<br>");
document.write(arr2[2], "<br>");

배열을 선언하지 않고 초기화

let arr3 = [100, 200, 300]

document.write(arr3[0],"<br>");
document.write(arr3[1],"<br>");
document.write(arr3[3],"<br>");

배열의 크기

let arr4 = [100,200,300,400,500];

document.write(arr4.length);

배열 가져오기

let arr1 = [100, 200, 300, 400, 500, 700, 800, 900];

/*document.write(arrl[0],"<br>")
document.write(arrl[1],"<br>")
document.write(arrl[2],"<br>")
document.write(arrl[3],"<br>")
document.write(arrl[4],"<br>")
document.write(arrl[5],"<br>")
document.write(arrl[6],"<br>")
document.write(arrl[7],"<br>")
document.write(arrl[8],"<br>")
document.write(arrl[9],"<br>")
document.write(arrl[10],"<br>")*/

for(let i=0; i<=arr1.length; i++){
    document.write(arr1[i], "<br>");
}

배열의 합 구하기

let arr2 = [100, 200, 300, 400, 500];
let sum = 0;

for(let i = 0; i<arr2.length, i++){
    //arr2[0] = 100
    //arr2[1] = 200
    //arr2[2] = 300
    //arr2[3] = 400
    //arr2[4] = 500
    //arr2[5] = 600
    //arr2[6] = 700 
    //arr2[7] = 800
    //arr2[8] = 900
    sum = sum + arr2[i]
}
document.write(sum);

forEach 사용하기

const arr3 = [100,200,300,400,500,600,700,800,900];

arr3.forEach((element, index, array) => {
    document.write(element, "<br>");
    document.write(index, "<br>");
    document.write(array, "<br>");
})

for in 문

const arr3 = [100,200,300,400,500,600,700,800,900];
for(let i in arr3){
    document.write(arr3[i]);
}

for of 문

const arr3 = [100,200,300,400,500,600,700,800,900];
for(let i of arr3){
    document.write(i);
}

배열 비구조화 할당

let [x, y] = [100,200];

document.write(x);
document.write(y);
document.write("<br><br>");

[x, y] = [y, x]

document.write(x);
document.write(y);