JavaScript: Perform a binary search within an array

Last update on May 30 2022 10:07:23 (UTC/GMT +8 hours)

JavaScript Array: Exercise-18 with Solution

Write a JavaScript program to perform a binary search.

Note : A binary search or half-interval search algorithm finds the position of a specified input value within an array sorted by key value.

Sample array:
var items = [1, 2, 3, 4, 5, 7, 8, 9];
Expected Output:
console.log(binary_Search(items, 1)); //0
console.log(binary_Search(items, 5)); //4

Sample Solution:

HTML Code:

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Binary Search</title>
</head>
<body>
</body>
</html>

JavaScript Code:

function binary_Search(items, value){
    var firstIndex  = 0,
        lastIndex   = items.length - 1,
        middleIndex = Math.floor((lastIndex + firstIndex)/2);

    while(items[middleIndex] != value && firstIndex < lastIndex)
    {
       if (value < items[middleIndex])
        {
            lastIndex = middleIndex - 1;
        } 
      else if (value > items[middleIndex])
        {
            firstIndex = middleIndex + 1;
        }
        middleIndex = Math.floor((lastIndex + firstIndex)/2);
    }

 return (items[middleIndex] != value) ? -1 : middleIndex;
}
var items = [1, 2, 3, 4, 5, 7, 8, 9];
console.log(binary_Search(items, 1));   
console.log(binary_Search(items, 5));

Sample Output:

0
4

Flowchart:

ES6 Version:

function binary_Search(items, value){
    let firstIndex  = 0;
    let lastIndex   = items.length - 1;
    let middleIndex = Math.floor((lastIndex + firstIndex)/2);

    while(items[middleIndex] != value && firstIndex < lastIndex)
    {
       if (value < items[middleIndex])
        {
            lastIndex = middleIndex - 1;
        } 
      else if (value > items[middleIndex])
        {
            firstIndex = middleIndex + 1;
        }
        middleIndex = Math.floor((lastIndex + firstIndex)/2);
    }

    return (items[middleIndex] != value) ? -1 : middleIndex;
}
const items = [1, 2, 3, 4, 5, 7, 8, 9];
console.log(binary_Search(items, 1));   
console.log(binary_Search(items, 5));

Live Demo:

See the Pen JavaScript - Perform a binary search within an array - array-ex- 18 by w3resource (@w3resource) on CodePen.

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Next: write a JavaScript program to compute the sum of each individual index value from the given arrays.

JavaScript: Tips of the Day

How to insert an item into an array at a specific index (JavaScript)?

What you want is the splice function on the native array object.

arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert). In this example we will create an array and add an element to it into index 2:

var arr = []; arr[0] = "Jani"; arr[1] = "Hege"; arr[2] = "Stale"; arr[3] = "Kai Jim"; arr[4] = "Borge"; console.log(arr.join()); arr.splice(2, 0, "Lene"); console.log(arr.join());

Ref: https://bit.ly/2BXbp04