JS: String.prototype.indexOf

str.indexOf(search_str)

Return the start index of first occurrence of search_str. Return -1 if not found.

str.indexOf(search_str, start_search_pos)

Start search at start_search_pos.

const ss = "abcabc";

// return index where first b occurs
console.log( ss.indexOf ( "b" ) ); // 1

// start at index 1 (including index 1)
console.log( ss.indexOf ( "b", 1 ) ); // 1

// start at index 2
console.log( ss.indexOf ( "b", 2 ) ); // 4

// more than 1 char
console.log( ss.indexOf ( "bc", 2 ) ); // 4

// example of not found, returns -1
console.log( ss.indexOf ( "xy" ) ); // -1