binary_search created by ValentynaGorbachenko - https://repl.it/C74Z/12

binary_search.js

 // O(log(n)) - time complexity
 // O(n) - space complexity
 
 function binarySearch(arr,val){
 	if (arr.length === 0){return -1;}
 	var li = 0;
 	var hi = arr.length-1;
 
 	while(li<=hi){
 		var mid = Math.floor(li+(hi-li)/2);
 		// console.log(li, mid, hi);
 		if (arr[mid] === val){
 			return mid;
 		}else if (arr[mid]<val) {
 			li = mid+1;
 		} else if (arr[mid]>val){
 			hi = mid-1;
 		}
 	}
 	return -1;
 }
 
 var arr = [0,1,3,5,9,12,20];
 console.log("array [0,1,3,5,9,12,20] has 12 in position ",binarySearch(arr, 12));
 
 
 function binarySearchRecursively(arr, val, li, hi){
 	if(!arr.length) {return -1;}
 	if (li === undefined && hi === undefined){
 		li = 0;
 		hi = arr.length -1;
 	}
 	if (li<=hi) {
 		var mid = Math.floor(li+(hi-li)/2);
 		// var mid = Math.floor((hi+li)/2);
 		// console.log(li, mid, hi);
	 	if ( arr[mid] == val) {return mid;}
	 	if(arr[mid]> val){
	 		return binarySearchRecursively(arr, val, li, mid-1);
	 	}
	 	return binarySearchRecursively(arr, val, mid+1, hi);
 	}
 	return -1;
 }
 
 var arr2 = [0,1,3,5,9,12,20];
 console.log("array 2 [0,1,3,5,9,12,20] has 1 in position ",binarySearchRecursively(arr2, 1));