JavaScript Program for Linear Search with Example

A JavaScript program for linear search checks each element in an array one by one using a for loop and returns the index if the element matches, like function linearSearch(arr, target) { for (let i = 0; i < arr.length; i++) { if (arr[i] === target) return i; } return -1; }.

Examples

Input[3, 5, 7, 9], target=7

Output2

Input[10, 20, 30, 40], target=25

Output-1

Input[], target=1

Output-1

How to Think About It

To find a target value in a list, start from the first item and check each one in order. If you find the target, stop and return its position. If you reach the end without finding it, return -1 to show it's not there.

Algorithm

1

Start from the first element of the array.

2

Compare the current element with the target value.

3

If they match, return the current index.

4

If not, move to the next element.

5

Repeat until the end of the array.

6

If the target is not found, return -1.

Code

javascript

function linearSearch(arr, target) {
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] === target) {
      return i;
    }
  }
  return -1;
}

console.log(linearSearch([3, 5, 7, 9], 7)); // 2
console.log(linearSearch([10, 20, 30, 40], 25)); // -1
console.log(linearSearch([], 1)); // -1

Output

2
-1
-1

Dry Run

Let's trace searching for 7 in [3, 5, 7, 9] through the code

1

Check first element

Compare arr[0] = 3 with target 7 → not equal

2

Check second element

Compare arr[1] = 5 with target 7 → not equal

3

Check third element

Compare arr[2] = 7 with target 7 → equal, return index 2

Index	Array Value	Comparison Result
0	3	No
1	5	No
2	7	Yes - Found

Why This Works

Step 1: Loop through array

The for loop goes through each element one by one to check all possible matches.

Step 2: Compare elements

Each element is compared with the target using === to find an exact match.

Step 3: Return index or -1

If a match is found, the function returns the index immediately; otherwise, it returns -1 after checking all elements.

Alternative Approaches

Using Array.prototype.indexOf

javascript

function linearSearch(arr, target) {
  return arr.indexOf(target);
}

console.log(linearSearch([3, 5, 7, 9], 7)); // 2

This is simpler and uses built-in method but less flexible for custom comparisons.

Using while loop

javascript

function linearSearch(arr, target) {
  let i = 0;
  while (i < arr.length) {
    if (arr[i] === target) return i;
    i++;
  }
  return -1;
}

console.log(linearSearch([3, 5, 7, 9], 7)); // 2

Uses a while loop instead of for loop; functionally same but different style.

Complexity: O(n) time, O(1) space

Time Complexity

The algorithm checks each element once, so time grows linearly with array size.

Space Complexity

Only a few variables are used, so extra space stays constant regardless of input size.

Which Approach is Fastest?

Using indexOf is fastest for simple equality checks, but custom loops allow more flexibility.

Approach	Time	Space	Best For
For loop linear search	O(n)	O(1)	Custom conditions and clarity
Array.indexOf	O(n)	O(1)	Simple equality search
While loop linear search	O(n)	O(1)	Alternative loop style