JS Practice — Built-in Objects

Array.prototype.indexOf() — returns -1 when not found

📖 Usage Example

const arr = [1, 2, 3]
arr.indexOf(99)  // → -1  (not found)

indexOf() returns -1 when the value is not present — always check for this sentinel.

Array.prototype.indexOf() — -1 sentinel

By convention, -1 means "not found" for all index-returning array methods. Always check the return value before using it as an index.

Challenge: Implement indexOf5(arr) that returns the index of 5 in the array, or -1 if not present.

indexOf5([1, 5, 3])  // → 1
indexOf5([1, 2, 3])  // → -1

💡 Hints (2)