Linear search in a JavaScript array

The linear search algorithm is a simple and straightforward way to find the index of a given element in an array. It works by iterating over each element in the array and comparing it with the target element.

A linear search has a time complexity of O(n), where n is the number of elements in the array. This means that the time it takes to find the element is directly proportional to the size of the array.

Implementing a linear search is relatively easy, as it only requires a for...in loop to iterate over the elements and compare them with the target element. If the element is found, the index is returned. As the for...in loop iterates over the indexes as strings, the unary + operator is used to convert the index to a number before returning it.

If the element is not found after iterating over the entire array, -1 is returned to indicate that the element is not present.

const linearSearch = (arr, item) => {
  for (const i in arr)
    if (arr[i] === item) return +i;

  return -1;
};

linearSearch([2, 9, 9], 9); // 1
linearSearch([2, 9, 9], 7); // -1