# Binary search

Finds the index of a given element in a sorted array using the binary search algorithm.

- Declare the left and right search boundaries,
`l`

and`r`

, initialized to`0`

and the`length`

of the array respectively. - Use a
`while`

loop to repeatedly narrow down the search subarray, using`Math.floor()`

to cut it in half. - Return the index of the element if found, otherwise return
`-1`

.

const binarySearch = (arr, item) => { let l = 0, r = arr.length - 1; while (l <= r) { const mid = Math.floor((l + r) / 2); const guess = arr[mid]; if (guess === item) return mid; if (guess > item) r = mid - 1; else l = mid + 1; } return -1; }; binarySearch([1, 2, 3, 4, 5], 1); // 0 binarySearch([1, 2, 3, 4, 5], 5); // 4 binarySearch([1, 2, 3, 4, 5], 6); // -1