자바스크립트 : 기본 규칙

01. 배열 속성 : length : 배열의 길이 구하기 : 반환(숫자)
02. 배열 메서드 : join() : 배열 요소의 문자열을 결합 : 반환(문자열) : ⭐⭐⭐
03. 배열 메서드 : push() : 배열 마지막 요소에 추가 : 반환(숫자) : ⭐⭐
03. 배열 메서드 : pop() : 배열 마지막 요소를 삭제 : 반환(삭제된 요소)
04. 배열 : unshift() : 배열 처음 요소에 추가 : 반환(숫자)
04. 배열 : shift() : 배열 처음 요소 삭제 : 반환(삭제된 요소)
05. 배열 : reverse() : 배열 요소의 순서를 반대로 정렬 : 반환(배열)
05. 배열 : sort() : 배열 요소를 정렬할 때 : 반환(배열)
06. 배열 : concat() : 배열 요소를 결합할 때 : 반환(배열)
07. 배열 : reduce() : 배열 요소를 하나로 정리 : 반환(결과값)
07. 배열 : reduceRight() : 배열 요소를 하나로 정리 : 반환(결과값)
08. 배열 : slice() : 배열 요소를 다른 요소로 변경 : 반환(배열) : ⭐⭐
09. 배열 : splice() : 배열 요소를 다른 요소로 변경 : 반환(배열) : ⭐⭐
10. 배열 : indexOf() : 배열 요소를 검색할 때 : 반환(숫자)
10. 배열 : lastIndexOf() : 배열 요소를 끝에서 검색할 때 : 반환(숫자)
10. 배열 : includes() : 배열 요소를 검색할 때 : 반환(불린)
11. 배열 : find() : 배열 요소를 검색할 때 : 반환(요소) : ⭐⭐
11. 배열 : findIndex() : 배열 요소를 검색할 때 : 반환(숫자)
12. 배열 : filter() : 조건에 만족하는 배열 요소를 검색할 때 : 반환(배열) : ⭐⭐
13. 배열 : map() : 배열 요소를 추출하여 새로운 배열로 만듦 : 반환(배열)
14. 배열 : Array.from() : 문자열을 배열로 변환합니다 : 반환(결괏값)

01. 배열 속성 : length : 배열의 길이 구하기 : 반환(숫자)

length는 배열의 길이를 구할 수 있는 속성입니다. 배열.length의 형식으로 사용합니다.

번호	기본값	메서드	리턴값

//01
const arrNum = [100, 200, 300, 400, 500];

document.querySelector(".sample01_N1").innerHTML = "1";
document.querySelector(".sample01_Q1").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample01_M1").innerHTML = "length";
document.querySelector(".sample01_P1").innerHTML = arrNum.length;   //5

//02
const arrTxt = ['a', 'b', 'c', 'd', 'e'];

document.querySelector(".sample01_N2").innerHTML = "2";
document.querySelector(".sample01_Q2").innerHTML = "['a', 'b', 'c', 'd', 'e']";
document.querySelector(".sample01_M2").innerHTML = "length";
document.querySelector(".sample01_P2").innerHTML = arrTxt.length;   //5

//03
const arr = [1, 2, ['a', 'b']];

document.querySelector(".sample01_N3").innerHTML = "3";
document.querySelector(".sample01_Q3").innerHTML = "[1, 2, ['a', 'b']]";
document.querySelector(".sample01_M3").innerHTML = "length";
document.querySelector(".sample01_P3").innerHTML = arr.length;  //3

02. 배열 메서드 : join() : 배열 요소의 문자열을 결합 : 반환(문자열) : ⭐⭐⭐

join() 메서드는 배열 요소의 문자열을 결합한 뒤 반환하여 줍니다. ()괄호 안에 문자를 넣어 작성한 경우, 배열의 요소 사이에 해당 문자를 넣어 결합한 뒤 반환해 줍니다.

번호	기본값	메서드	리턴값

const arrNum = [100, 200, 300, 400, 500];
const text1 = arrNum.join('');
const text2 = arrNum.join(' ');
const text3 = arrNum.join('♠');
const text4 = arrNum.join('-');

//01
document.querySelector(".sample02_N1").innerHTML = "1";
document.querySelector(".sample02_Q1").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample02_M1").innerHTML = "join('')";
document.querySelector(".sample02_P1").innerHTML = text1;


//02
document.querySelector(".sample02_N2").innerHTML = "2";
document.querySelector(".sample02_Q2").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample02_M2").innerHTML = "join(' ')";
document.querySelector(".sample02_P2").innerHTML = text2;

//03
document.querySelector(".sample02_N3").innerHTML = "3";
document.querySelector(".sample02_Q3").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample02_M3").innerHTML = "join('♠')";
document.querySelector(".sample02_P3").innerHTML = text3;

//04
document.querySelector(".sample02_N4").innerHTML = "4";
document.querySelector(".sample02_Q4").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample02_M4").innerHTML = "join('-')";
document.querySelector(".sample02_P4").innerHTML = text4;

03. 배열 메서드 : push() / pop()

push() 메서드는 배열의 마지막 요소에 추가하는 메서드이며, 추가한 뒤 배열의 길이값을 숫자로 반환합니다. 메서드의 괄호 안에는 추가하고자 하는 요소를 작성합니다.
pop() 메서드는 배열의 마지막 요소를 삭제하는 메서드이며, 삭제한 요소를 리턴값으로 반환합니다.

번호	기본값	메서드	리턴값	결과값

//01
const arrNum = [100, 200, 300, 400, 500];
const arrPush = arrNum.push(600);

document.querySelector(".sample03_N1").innerHTML = "1";
document.querySelector(".sample03_Q1").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample03_M1").innerHTML = "push(600)";
document.querySelector(".sample03_P1").innerHTML = arrPush; //6
document.querySelector(".sample03_A1").innerHTML = arrNum;  //100,200,300,400,500,600

//02
const arrNum2 = [100, 200, 300, 400, 500];
const arrPop = arrNum2.pop();

document.querySelector(".sample03_N2").innerHTML = "2";
document.querySelector(".sample03_Q2").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample03_M2").innerHTML = "pop()";
document.querySelector(".sample03_P2").innerHTML = arrPop;  //500
document.querySelector(".sample03_A2").innerHTML = arrNum2; //100,200,300,400

04. 배열 메서드 : unshift() / shift()

unshift() 메서드는 배열 처음 요소에 추가, shift()메서드는 배열 처음 요소를 삭제합니다.

번호	기본값	메서드	리턴값	결과값

const arrNum1 = [100, 200, 300, 400, 500];
const arrNumUnshift = arrNum1.unshift(600);

document.querySelector(".sample04_N1").innerHTML = "1";
document.querySelector(".sample04_Q1").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample04_M1").innerHTML = "unshift(600)";
document.querySelector(".sample04_P1").innerHTML = arrNumUnshift; //6
document.querySelector(".sample04_A1").innerHTML = arrNum1;  //600,100,200,300,400,500

const arrNum2 = [100, 200, 300, 400, 500];
const arrNumShift = arrNum2.shift();

document.querySelector(".sample04_N2").innerHTML = "1";
document.querySelector(".sample04_Q2").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample04_M2").innerHTML = "shift()";
document.querySelector(".sample04_P2").innerHTML = arrNumShift; //100
document.querySelector(".sample04_A2").innerHTML = arrNum2;  //200,300,400,500

05. 배열 메서드 : reverse() / sort()

reverse() 메서드는 순서를 반대로 정렬, sort() 메서드는 배열 요소를 정렬합니다.

번호	기본값	메서드	리턴값

const arrNum1 = [400, 500, 300, 100, 500];
const arrNumReverse = arrNum1.reverse();

document.querySelector(".sample05_N1").innerHTML = "1";
document.querySelector(".sample05_Q1").innerHTML = "[400, 500, 300, 100, 500]";
document.querySelector(".sample05_M1").innerHTML = "reverse()";
document.querySelector(".sample05_P1").innerHTML = arrNumReverse; //500,400,300,200,100

const arrNum2 = [400, 500, 300, 100, 500];
const arrNumSort2 = arrNum2.sort();

document.querySelector(".sample05_N2").innerHTML = "2";
document.querySelector(".sample05_Q2").innerHTML = "[400, 500, 300, 100, 500]";
document.querySelector(".sample05_M2").innerHTML = "sort()";
document.querySelector(".sample05_P2").innerHTML = arrNumSort2; //100,200,300,400,500

const arrNum3 = [400, 500, 300, 100, 500];
const arrNumSort3 = arrNum3.sort(function(a,b){return b-a});

document.querySelector(".sample05_N3").innerHTML = "3";
document.querySelector(".sample05_Q3").innerHTML = "[400, 500, 300, 100, 500]";
document.querySelector(".sample05_M3").innerHTML = "sort(function(a,b){return b-a})";
document.querySelector(".sample05_P3").innerHTML = arrNumSort3; //500,400,300,200,100

const arrNum4 = [400, 500, 300, 100, 500];
const arrNumSort4 = arrNum4.sort(function(a,b){return a-b});

document.querySelector(".sample05_N4").innerHTML = "4";
document.querySelector(".sample05_Q4").innerHTML = "[400, 500, 300, 100, 500]";
document.querySelector(".sample05_M4").innerHTML = "sort(function(a,b){return a-b})";
document.querySelector(".sample05_P4").innerHTML = arrNumSort4; //100,200,300,400,500

const arrNum5 = ['c', 'b', 'e', 'd', 'a'];
const arrNumSort5 = arrNum5.sort(function(a,b){return a.localeCompare(b)});

document.querySelector(".sample05_N5").innerHTML = "5";
document.querySelector(".sample05_Q5").innerHTML = "['c', 'b', 'e', 'd', 'a']";
document.querySelector(".sample05_M5").innerHTML = "sort(function(a,b){return a.localeCompare(b)})";
document.querySelector(".sample05_P5").innerHTML = arrNumSort5; //a,b,c,d,e

const arrNum6 = ['c', 'b', 'e', 'd', 'a'];
const arrNumSort6 = arrNum5.sort(function(a,b){return b.localeCompare(a)});

document.querySelector(".sample05_N6").innerHTML = "6";
document.querySelector(".sample05_Q6").innerHTML = "['c', 'b', 'e', 'd', 'a']";
document.querySelector(".sample05_M6").innerHTML = "sort(function(a,b){return b.localeCompare(a)})";
document.querySelector(".sample05_P6").innerHTML = arrNumSort6; //e,d,c,b,a

06. 배열 메서드 : concat()

concat() 메서드는 배열 요소를 결합합니다.

번호	기본값	메서드	리턴값

const arrNum1 = [100, 200, 300];
const arrNum2 = [400, 500, 600];
const arrConcat = arrNum1.concat(arrNum2);

document.querySelector(".sample06_N1").innerHTML = "1";
document.querySelector(".sample06_Q1").innerHTML = "[100, 200, 300], [400, 500, 600]";
document.querySelector(".sample06_M1").innerHTML = "arrNum1.concat(arrNum2)";
document.querySelector(".sample06_P1").innerHTML = arrConcat; //100,200,300,400,500,600

const arrSpread = [...arrNum1, ...arrNum2];

document.querySelector(".sample06_N2").innerHTML = "2";
document.querySelector(".sample06_Q2").innerHTML = "[100, 200, 300], [400, 500, 600]";
document.querySelector(".sample06_M2").innerHTML = "[...arrNum1, ...arrNum2]";
document.querySelector(".sample06_P2").innerHTML = arrSpread; //100,200,300,400,500,600

07. 배열 메서드 : reduce() / reduceRight()

reduce() 메서드는 배열 요소를 순서대로 합치고, reduceRight()메서드는 배열 요소를 반대로 합칩니다.

번호	기본값	메서드	리턴값

const arrNum1 = [100, 200, 300, 400, 500];
const arrNumReduce1 = arrNum1.reduce(element => element);

document.querySelector(".sample07_N1").innerHTML = "1";
document.querySelector(".sample07_Q1").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample07_M1").innerHTML = "reduce(element => element)";
document.querySelector(".sample07_P1").innerHTML = arrNumReduce1; //100

const arrNum2 = [100, 200, 300, 400, 500];
const arrNumReduce2 = arrNum1.reduce( (p,c) => p + c);

document.querySelector(".sample07_N2").innerHTML = "2";
document.querySelector(".sample07_Q2").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample07_M2").innerHTML = "reduce( (p,c) => p + c)";
document.querySelector(".sample07_P2").innerHTML = arrNumReduce2; //1500

const arrNum3 = [100, 200, 300, 400, 500];
let sum = 0;

for(let i=0; i<arrNum1.length; i++){
    sum += arrNum1[i];
};
document.querySelector(".sample07_N3").innerHTML = "3";
document.querySelector(".sample07_Q3").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample07_M3").innerHTML = "for()";
document.querySelector(".sample07_P3").innerHTML = sum; //1500

const arrNum4 = [[100,200],[300,400]];
const arrNumReduce4 = arrNum4.reduce((p,c) => p.concat(c));

document.querySelector(".sample07_N4").innerHTML = "4";
document.querySelector(".sample07_Q4").innerHTML = "[[100,200],[30,400]]";
document.querySelector(".sample07_M4").innerHTML = "reduce((p,c) => p.concat(c))";
document.querySelector(".sample07_P4").innerHTML = arrNumReduce4; //100,200,300,400

const arrNum5 = ["javascript", "react", "vue"];
const arrNumReduce5 = arrNum5.reduceRight((p,c) => p+c);

document.querySelector(".sample07_N5").innerHTML = "4";
document.querySelector(".sample07_Q5").innerHTML = '["javascript", "react", "vue"]';
document.querySelector(".sample07_M5").innerHTML = "reduceRight((p,c) => p+c)";
document.querySelector(".sample07_P5").innerHTML = arrNumReduce5; //vuereactjavascript

08. 배열 메서드 : slice()

slice() 메서드는 배열 요소의 특정 값을 출력합니다. 원래 배열의 값 변화X

번호	기본값	메서드	리턴값

const arrNum = [100, 200, 300, 400, 500];
const result1 = arrNum.slice(2);

document.querySelector(".sample08_N1").innerHTML = "1";
document.querySelector(".sample08_Q1").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample08_M1").innerHTML = "slice(2)";
document.querySelector(".sample08_P1").innerHTML = result1; //300,400,500

const result2 = arrNum.slice(2, 3);

document.querySelector(".sample08_N2").innerHTML = "2";
document.querySelector(".sample08_Q2").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample08_M2").innerHTML = "slice(2, 3)";
document.querySelector(".sample08_P2").innerHTML = result2; //300

const result3 = arrNum.slice(2, 4);

document.querySelector(".sample08_N3").innerHTML = "3";
document.querySelector(".sample08_Q3").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample08_M3").innerHTML = "slice(2, 4)";
document.querySelector(".sample08_P3").innerHTML = result3; //300,400

const result4 = arrNum.slice(2, 5);

document.querySelector(".sample08_N4").innerHTML = "4";
document.querySelector(".sample08_Q4").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample08_M4").innerHTML = "slice(2, 5)";
document.querySelector(".sample08_P4").innerHTML = result4; //300,400,500

const result5 = arrNum.slice(-2);

document.querySelector(".sample08_N5").innerHTML = "5";
document.querySelector(".sample08_Q5").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample08_M5").innerHTML = "slice(-2)";
document.querySelector(".sample08_P5").innerHTML = result5; //400,500

const result6 = arrNum.slice(-2, 5);

document.querySelector(".sample08_N6").innerHTML = "6";
document.querySelector(".sample08_Q6").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample08_M6").innerHTML = "slice(-2, 5)";
document.querySelector(".sample08_P6").innerHTML = result6; //400,500

09. 배열 메서드 : splice()

splice() 메서드는 배열 요소를 다른 요소로 변경합니다. 원래 배열의 값 변화

번호	기본값	메서드	리턴값	결과값

const arrNum = [100, 200, 300, 400, 500];
const result = arrNum.splice(2);

document.querySelector(".sample09_N1").innerHTML = "1";
document.querySelector(".sample09_Q1").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample09_M1").innerHTML = "arrNum.splice(2)";
document.querySelector(".sample09_P1").innerHTML = result;//300,400,500
document.querySelector(".sample09_A1").innerHTML = arrNum;//100,200

const arrNum2 = [100, 200, 300, 400, 500];
const result2 = arrNum2.splice(2, 3);

document.querySelector(".sample09_N2").innerHTML = "2";
document.querySelector(".sample09_Q2").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample09_M2").innerHTML = "arrNum2.splice(2,3)";
document.querySelector(".sample09_P2").innerHTML = result2;//300,400,500
document.querySelector(".sample09_A2").innerHTML = arrNum2;//100,200

const arrNum3 = [100, 200, 300, 400, 500];
const result3 = arrNum3.splice(2, 3, 'javascript');

document.querySelector(".sample09_N3").innerHTML = "3";
document.querySelector(".sample09_Q3").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample09_M3").innerHTML = "arrNum3.splice(2,3, 'javascript')";
document.querySelector(".sample09_P3").innerHTML = result3;//300,400,500
document.querySelector(".sample09_A3").innerHTML = arrNum3;//100,200,javascript

const arrNum4 = [100, 200, 300, 400, 500];
const result4 = arrNum4.splice(1, 1, 'javascript');

document.querySelector(".sample09_N4").innerHTML = "4";
document.querySelector(".sample09_Q4").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample09_M4").innerHTML = "arrNum4.splice(1, 1, 'javascript')";
document.querySelector(".sample09_P4").innerHTML = result4;//200
document.querySelector(".sample09_A4").innerHTML = arrNum4;//100,javascript,300,400,500

const arrNum5 = [100, 200, 300, 400, 500];
const result5 = arrNum5.splice(1, 0, 'javascript');

document.querySelector(".sample09_N5").innerHTML = "5";
document.querySelector(".sample09_Q5").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample09_M5").innerHTML = "arrNum5.splice(1, 0, 'javascript')";
document.querySelector(".sample09_P5").innerHTML = result5;//_
document.querySelector(".sample09_A5").innerHTML = arrNum5;//100,javascript,200,300,400,500

const arrNum6 = [100, 200, 300, 400, 500];
const result6 = arrNum6.splice(0, 4, 'javascript');

document.querySelector(".sample09_N6").innerHTML = "6";
document.querySelector(".sample09_Q6").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample09_M6").innerHTML = "arrNum6.splice(0, 4, 'javascript')";
document.querySelector(".sample09_P6").innerHTML = result6;//100,200,300,400
document.querySelector(".sample09_A6").innerHTML = arrNum6;//javascript,500

10. 배열 메서드 : indexOf() / lastIndexOf() / includes()

indexOf(), includes() 메서드는 배열 요소를 배열 요소를 검색하고, lastIndexOf() 메서드는 배열 요소를 뒤에서부터 검색합니다.

번호	기본값	메서드	리턴값

const arrNum1 = [100, 200, 300, 400, 500];
const arrIndex1 = arrNum1.indexOf(200);

document.querySelector(".sample10_N1").innerHTML = "1";
document.querySelector(".sample10_Q1").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample10_M1").innerHTML = "indexOf(200)";
document.querySelector(".sample10_P1").innerHTML = arrIndex1; //1

const arrNum2 = [100, 200, 300, 400, 500];
const arrIndex2 = arrNum2.indexOf(300);

document.querySelector(".sample10_N2").innerHTML = "2";
document.querySelector(".sample10_Q2").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample10_M2").innerHTML = "indexOf(300)";
document.querySelector(".sample10_P2").innerHTML = arrIndex2; //2

const arrNum3 = [100, 200, 300, 400, 500];
const arrIndex3 = arrNum3.indexOf(600);

document.querySelector(".sample10_N3").innerHTML = "3";
document.querySelector(".sample10_Q3").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample10_M3").innerHTML = "indexOf(600)";
document.querySelector(".sample10_P3").innerHTML = arrIndex3; //-1

const arrNum4 = [100, 200, 300, 400, 500];
const arrIndex4 = arrNum4.lastIndexOf(200);

document.querySelector(".sample10_N4").innerHTML = "4";
document.querySelector(".sample10_Q4").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample10_M4").innerHTML = "lastIndexOf(200)";
document.querySelector(".sample10_P4").innerHTML = arrIndex4; //1

const arrNum5 = [100, 200, 300, 400, 200];
const arrIndex5 = arrNum5.includes(200);

document.querySelector(".sample10_N5").innerHTML = "5";
document.querySelector(".sample10_Q5").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample10_M5").innerHTML = "includes(200)";
document.querySelector(".sample10_P5").innerHTML = arrIndex5; //true

const arrNum6 = [100, 200, 300, 400, 500];
const arrIndex6 = arrNum5.includes(600);

document.querySelector(".sample10_N6").innerHTML = "6";
document.querySelector(".sample10_Q6").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample10_M6").innerHTML = "includes(600)";
document.querySelector(".sample10_P6").innerHTML = arrIndex6; //false

11. 배열 메서드 : find() / findIndex()

find(), findIndex() 메서드는 배열 요소에서 특정 값을 찾을 수 있습니다.

번호	기본값	메서드	리턴값

const arrNum = [100, 200, 300, 400, 500];
// const result = arrNum.find(function(element){
//     return element === 300;
// });
//생략
// const result = arrNum.find((element) => {
//     return element === 300;
// });
//생략
// const result = arrNum.find(element => {
//     return element === 300;
// });
//생략
const result = arrNum.find(e => e === 300);

document.querySelector(".sample11_N1").innerHTML = "1";
document.querySelector(".sample11_Q1").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample11_M1").innerHTML = "find(e => e === 300)";
document.querySelector(".sample11_P1").innerHTML = result; //300

const result2 = arrNum.find(e => e === 600);

document.querySelector(".sample11_N2").innerHTML = "2";
document.querySelector(".sample11_Q2").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample11_M2").innerHTML = "find(e => e === 300)";
document.querySelector(".sample11_P2").innerHTML = result2; //undefined

const arrText = ['javascript', 'jquery', 'react'];
const result3 = arrText.find(el => el === 'javascript');

document.querySelector(".sample11_N3").innerHTML = "3";
document.querySelector(".sample11_Q3").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample11_M3").innerHTML = "find(el => el === 'javascript')";
document.querySelector(".sample11_P3").innerHTML = result3; //javascript

const result4 = arrText.findIndex(el => el === 'javascript');

document.querySelector(".sample11_N4").innerHTML = "4";
document.querySelector(".sample11_Q4").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample11_M4").innerHTML = "findIndex(el => el === 'javascript')";
document.querySelector(".sample11_P4").innerHTML = result4; //0

const result5 = arrText.findIndex(el => el === 'html');

document.querySelector(".sample11_N5").innerHTML = "5";
document.querySelector(".sample11_Q5").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample11_M5").innerHTML = "findIndex(el => el === 'html')";
document.querySelector(".sample11_P5").innerHTML = result5; //-1

12. 배열 메서드 : filter()

filter() 메서드는 배열 요소 값을 찾을 수 있습니다. (find와의 차이점은 조건식을 걸 수 있다는 점 => 활용성 UP)

번호	기본값	메서드	리턴값

const arrNum = [100, 200, 300, 400, 500];
const result = arrNum.filter(el => el === 300);

document.querySelector(".sample12_N1").innerHTML = "1";
document.querySelector(".sample12_Q1").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample12_M1").innerHTML = "filter(el => el === 300)";
document.querySelector(".sample12_P1").innerHTML = result; //300

const arrNum2 = [100, 200, 300, 400, 500];
const result2 = arrNum2.filter(el => el === 600);

document.querySelector(".sample12_N2").innerHTML = "2";
document.querySelector(".sample12_Q2").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample12_M2").innerHTML = "filter(el => el === 600)";
document.querySelector(".sample12_P2").innerHTML = result2; //_

const arrNum3 = [100, 200, 300, 400, 500];
const result3 = arrNum2.filter(el => el >= 300);

document.querySelector(".sample12_N3").innerHTML = "3";
document.querySelector(".sample12_Q3").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample12_M3").innerHTML = "filter(el => el >= 300)";
document.querySelector(".sample12_P3").innerHTML = result3; //300,400,500

13. 배열 메서드 : map()

map() 메서드는 배열 요소를 추출하여 새로운 배열로 만듭니다.

번호	기본값	메서드	리턴값

const arrNum = [100, 200, 300, 400, 500];
    const result = arrNum.map(el => el);

document.querySelector(".sample13_N1").innerHTML = "1";
document.querySelector(".sample13_Q1").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample13_M1").innerHTML = "map(el => el)";
document.querySelector(".sample13_P1").innerHTML = result; //100,200,300,400,500

const arrNum2 = [100, 200, 300, 400, 500];
const result2 = arrNum2.map(el => el + 'j');

document.querySelector(".sample13_N2").innerHTML = "2";
document.querySelector(".sample13_Q2").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample13_M2").innerHTML = "map(el => el + 'j')";
document.querySelector(".sample13_P2").innerHTML = result2; //100j,200j,300j,400j,500j

const arrNum3 = [100, 200, 300, 400, 500];
const result3 = arrNum3.map(el => el + 100);

document.querySelector(".sample13_N3").innerHTML = "3";
document.querySelector(".sample13_Q3").innerHTML = "[100, 200, 300, 400, 500]";
document.querySelector(".sample13_M3").innerHTML = "map(el => el + 100)";
document.querySelector(".sample13_P3").innerHTML = result3; //200,300,400,500,600

const arrNum4 = [{a: 100}, {a: 200}, {a: 300}];
const result4 = arrNum4.map(el => el.a);

document.querySelector(".sample13_N4").innerHTML = "4";
document.querySelector(".sample13_Q4").innerHTML = "[{a: 100}, {b: 200}, {c: 300}]";
document.querySelector(".sample13_M4").innerHTML = "map(el => el.a)";
document.querySelector(".sample13_P4").innerHTML = result4; //100,200,300

14. 배열 메서드 : Array.from()

Array.from() 메서드는 문자열을 하나씩 쪼개 배열로 만들어 줍니다.

번호	기본값	메서드	리턴값

const text = "javascript";
const result = Array.from(text);
// 문자열을 하나식 쪼개 배열로 만들어 줍니다.

document.querySelector(".sample14_N1").innerHTML = "1";
document.querySelector(".sample14_Q1").innerHTML = "javascript";
document.querySelector(".sample14_M1").innerHTML = "Array.from(text)";
document.querySelector(".sample14_P1").innerHTML = result; //j,a,v,a,s,c,r,i,p,t
console.log(result);

const text2 = "javascript";
const result2 = Array.from(text2, el => el + '10');

document.querySelector(".sample14_N2").innerHTML = "2";
document.querySelector(".sample14_Q2").innerHTML = "javascript";
document.querySelector(".sample14_M2").innerHTML = "Array.from(text2, el => el + '10')";
document.querySelector(".sample14_P2").innerHTML = result2; //j10,a10,v10,a10,s10,c10,r10,i10,p10,t10
console.log(result2);

const text3 = "javascript";
const result3 = [...text3].map(el => el);

document.querySelector(".sample14_N3").innerHTML = "3";
document.querySelector(".sample14_Q3").innerHTML = "javascript";
document.querySelector(".sample14_M3").innerHTML = "[...text3].map(el => el)";
document.querySelector(".sample14_P3").innerHTML = result3; //j,a,v,a,s,c,r,i,p,t
console.log(result3);