Binary Search Algorithm

binarySearch.js

/* We can only use binary search if the input array of numbers is already sorted! */
let binarySearch = (target, numbers) => {
 /* find an apearance of target in numbers */
 
 /*
 ** we have lowLimit and highLimit of our range(numbers)
 ** so starting point is -1 (the 0th index)
 */ 
  
 let lowLimit = -1;
 let highLimit = numbers.length;
  
 /*
 ** if there isn't at least 1 index between lowLimit and highLimit,
 ** we've run out of guesses and the number must not be present
 */
  
	while ( (lowLimit + 1) < highLimit ) {
	 
		/*
		** find the index ~halfway between the lowLimit and highLimit
		** we have to round down, to avoid getting a "half index"
		*/

		let distance = highLimit - lowLimit;
		let halfDistance = Math.floor(distance / 2);
		let guessIndex = lowLimit + halfDistance;

		let guessValue = numbers[guessIndex];

		if (guessValue === target) {
			return true;
		}

		if (guessValue > target) {
			/* target is to the left, so move high boundary to the left */
			highLimit = guessIndex;
		} else {
			/* target is to the right, so move low boundary to the right */
			lowLimit = guessIndex;
		}
	 
	}
  
	return false;
}