메서드 (includes)

includes()

문자열 포함여부를 검색하여, 불린(true, false)를 반환한다.

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

    const str = "javascript reference";
    const currentStr1 = str1.includes("javascript")        // true
    const currentStr2 = str1.includes("j")                       // true
    const currentStr3 = str1.includes("b")                      // flase    //포함하고 있지 않기에 false
    const currentStr4 = str1.includes("reference")         // true
    const currentStr5 = str1.includes("reference", 1)     // true
    const currentStr6 = str1.includes("reference", 11)   // true
    const currentStr7 = str1.includes("reference", 12)   // false