Sequentially checks the target value in given list and match found.

Time Complexity: best : O(1) Worst: O(n)

Space Complexity: O(1)

function linearSearch(arr, target) {
    for (let i in arr) {
        if(arr[i] === target) return i;
    }
return -1;
};

linearSearch([1,2,3,4], 3);
> '2'
linearSearch([1,2,3,4], 5);
> -1

Linear search is best to use while searching in unsorted array.

JS indexOf(), includes(), find() & findIndex() implemented using linear search.