return -1 if target is not in array

utilities/javascript/binarySearch.js

@@ -12,15 +12,15 @@ function binarySearch(arr, target) {
             right = mid - 1;
         }
     }
-    return left;
+    return arr[left] === target ? left : -1;
 }
 
 console.log(binarySearch([1, 2, 3, 10], 1) === 0)
 console.log(binarySearch([1, 2, 3, 10], 2) === 1)
 console.log(binarySearch([1, 2, 3, 10], 3) === 2)
 console.log(binarySearch([1, 2, 3, 10], 10) === 3)
-console.log(binarySearch([1, 2, 3, 10], 9) === 3)
-console.log(binarySearch([1, 2, 3, 10], 4) === 3)
-console.log(binarySearch([1, 2, 3, 10], 0) === 0)
-console.log(binarySearch([1, 2, 3, 10], 11) === 3)
-console.log(binarySearch([5, 7, 8, 10], 3) === 0)
+console.log(binarySearch([1, 2, 3, 10], 9) === -1)
+console.log(binarySearch([1, 2, 3, 10], 4) === -1)
+console.log(binarySearch([1, 2, 3, 10], 0) === -1)
+console.log(binarySearch([1, 2, 3, 10], 11) === -1)
+console.log(binarySearch([5, 7, 8, 10], 3) === -1)