O(log n) Example

o(log_n).js

const array = [1, 2, 4, 8 ,16, 32, 64, 128, 256];
const number = 128;

function binarySearch(array, number) {
	let startIndex = 0;
	let endIndex = (array.length) - 1;
  
	while (startIndex <= endIndex) {
		let pivot = Math.floor((startIndex + endIndex)/2);
		
		if (array[pivot] === number) {
			return `Located ${number} at ${pivot}`;
		} else if (array[pivot] < number) {
			startIndex = pivot + 1;
		} else {
			endIndex = pivot - 1;
		}
	}
	return false;
}