JS Practice — Built-in Objects

String.prototype.indexOf() — first occurrence only

📖 Usage Example

const str = 'hello world'
str.indexOf('world')    // → 6
str.indexOf('xyz')      // → -1
str.indexOf('l')        // → 2

Use indexOf() to find the index of the first occurrence of a substring, returning -1 if not found.

String.prototype.indexOf() — First Occurrence

.indexOf() returns only the first occurrence. Use .lastIndexOf() for the last.

Challenge: Implement firstOccurrence(str, ch) using .indexOf().

firstOccurrence('abacaba', 'a') // → 0

💡 Hints (1)