Sometimes, we want to implement binary search in JavaScript.

In this article, we’ll look at how to implement binary search in JavaScript.

How to implement binary search in JavaScript?

To implement binary search in JavaScript, we can search for the index of the item according to the comparison of the item at different indexes starting at the middle of the array.

For instance, we write

const binarySearch = (arr, val) => {
  let start = 0;
  let end = arr.length - 1;

  while (start <= end) {
    let mid = Math.floor((start + end) / 2);

    if (arr[mid] === val) {
      return mid;
    }

    if (val < arr[mid]) {
      end = mid - 1;
    } else {
      start = mid + 1;
    }
  }
  return -1;
};

to define the binarySearch function.

In it, we define the start and end variables set to the first and last indexes of the sorted arr array.

Then we use a while loop to search for the item as long as start is less than or equal to end.

We get the mid array index with Math.floor.

And we check if arr[mid] is val.

If it is, we return the mid index.

If val is less than arr[mid], then we set end to mid - 1 to narrow down the search.

Otherwise, we set start to mid + 1 to narrow down the search.

If nothing is found then -1 is returned.

Conclusion

To implement binary search in JavaScript, we can search for the index of the item according to the comparison of the item at different indexes starting at the middle of the array.