JAVASCRIPT | 문자열 메서드 | indexOf( ) / lastIndexOf( )

문자열 메서드(검색)에 대해 알아보자 !

다양한 문자열 메서드 중 문자열에서 특정 문자의 위치를 찾고 숫자를 반환하는 indexOf() / lastIndexOf()에 대해 알아봅시다.

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01. indexOf( );

"문자열".indexOf(검색값)
"문자열".indexOf(검색값, 위치값)

const str1 = "javascript reference"

const currentstr1 = str1.indexOf("javascript");     //0(j가 0번째)
const currentstr2 = str1.indexOf("reference");     //11(r이 11번째)
const currentstr3 = str1.indexOf("j");     //0
const currentstr4 = str1.indexOf("a");     //1(중복일때는 제일 처음에 있는 위치값)
const currentstr5 = str1.indexOf("v");     //2
const currentstr6 = str1.indexOf("jquery");     //-1(데이터가 없을때는 -1 출력)
const currentstr7 = str1.indexOf("b");     //-1
const currentstr8 = str1.indexOf("javascript", 0);     //0
const currentstr9 = str1.indexOf("javascript", 1);     //-1
const currentstr10 = str1.indexOf("reference", 0);     //11
const currentstr11 = str1.indexOf("reference", 1);     //11
const currentstr12 = str1.indexOf("reference", 11);     //11
const currentstr13 = str1.indexOf("reference", 12);     //-1

02. lastIndexOf( );

"문자열".lastIndexOf(검색값)
"문자열".lastIndexOf(검색값, 위치값)

const str2 = "javascript reference"
    
const currentstr14 = str2.lastIndexOf("javascript");        //0
const currentstr15 = str2.lastIndexOf("reference");         //11
const currentstr16 = str2.lastIndexOf("j");                 //0
const currentstr17 = str2.lastIndexOf("a");                 //3(중복일때는 제일 뒤에 있는 위치값)
const currentstr18 = str2.lastIndexOf("v");                 //2
const currentstr19 = str2.lastIndexOf("jquery");            //-1
const currentstr20 = str2.lastIndexOf("b");                 //-1
const currentstr21 = str2.lastIndexOf("javascript", 0);     //0
const currentstr22 = str2.lastIndexOf("javascript", 1);     //0
const currentstr23 = str2.lastIndexOf("reference", 0);      //-1
const currentstr24 = str2.lastIndexOf("reference", 1);      //-1
const currentstr25 = str2.lastIndexOf("reference", 11);     //11
const currentstr26 = str2.lastIndexOf("reference", 12);     //11