How to implement binary search in typescript/JavaScript

In this article, I will discuss how to implement Binary Search in typescript.
Binary search compares the target value to the middle element of the array. If they are not equal, the half in which the target cannot lie is eliminated, and the search continues on the remaining half, again taking the middle element to compare to the target value, and repeating this until the target value is found. If the search ends with the remaining half being empty, the target is not in the array.

Pseudo Code
export function binarySearch(nums: Array<number>, key: number): number {
  let low = 0;
  let high = nums.length - 1;
  while (low <= high) {
    let mid = Math.floor((low + high) / 2);
    if (nums[mid] === key) {
      return mid + 1;
    if (key > nums[mid]) {
      low = mid + 1;
    } else {
      high = mid - 1;
  return -1;


How to implement binary search in typescript/JavaScript
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  • Worst-case performance O(log n)
  • Best-case performance O(1)
  • Average performance O(log n)
  • Worst-case space complexity

Further reading



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