JS: String.prototype.indexOf

By Xah Lee. Date: . Last updated: .

s.indexOf(str)

s.indexOf(str, start_search_index)

Return the index where the first occurrence of first char of str, starting search at start_search_index. start_search_index by default is 0. Returns -1 if not found.

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

Reference

ECMAScript 2015 §Text Processing#sec-string.prototype.indexof

JS String

  1. String Overview
  2. Template String
  3. Char, Code Unit, Code Point
  4. String Escape Sequence
  5. Unicode Escape Sequence
  6. String to Number
  7. Encode URL, Escape String
  8. Format Number
  9. Source Code Encoding
  10. Allowed Characters in Identifier
  11. String Object
  12. String.prototype
Liket it? Put $5 at patreon.

Or, Buy JavaScript in Depth

If you have a question, put $5 at patreon and message me.

Web Dev Tutorials

  1. HTML
  2. Visual CSS
  3. JS in Depth
  4. JS Reference
  5. DOM
  6. SVG
  7. Web Dev Blog