How to find index of element in array in js?

JavaScript provides several methods to find the index of an element in an array. The most commonly used methods are indexOf and findIndex.

Let’s take a closer look at each of these methods and how they work.

1. `indexOf` Method:

The indexOf method is a built-in Javascript array method that returns the first index at which a given element can be found in an array. If the element is not present in the array, it returns -1.

The syntax of the indexOf is as follows:

array.indexOf(elementToFind, startIndex);

where array is the array in which you want to search for the element, elementToFind is the element you are looking for, and startIndex is an optional parameter that specifies the index to start searching from.

If startIndex is not provided, the search starts from the beginning of the array.

Here’s an example of using indexOf:

const array = [1, 2, 3, 4, 5];
const element = 3;
const index = array.indexOf(element);
console.log(index); // Output: 2

In this example, the indexOf method is used to find the index of the element 3 in the array array. Since 3 is present at index 2 in the array, the output is 2.

It’s important to note that indexOf only returns the index of the first occurrence of the element that satisfies the condition. If there are multiple occurrences of the element in the array, only the index of the first occurrence will be returned.

2. `findIndex` Method:

The findIndex method is another built-in JavaScript array method that returns the index of the first element in the array that satisfies a given condition. If no such element is found, it returns -1.

The syntax for findIndex is as follows:

array.findIndex(callback(element, index, array));

where array is the array in which you want to search for the element, and callback is a callback function that specifies the condition. The callback function takes three arguments: element, which represents the current element being processed, index, which represents the index of the current element, and array, which represents the array on which the findIndex method was called.

Here’s an example of using findIndex:

const array = [{ id: 1 }, { id: 2 }, { id: 3 }, { id: 4 }, { id: 5 }];
const elementId = 3;
const index = array.findIndex((item) => item.id === elementId);
console.log(index); // Output: 2

In this example, the findIndex method is used to find the index of the element whose id property matches 3 in the array of objects array. Since the element with id equal to 3 is present at index 2 in the array, the output is 2.

It’s worth noting that findIndex returns the index of the first element that satisfies the condition. If there are multiple elements that satisfy the condition, only the index of the first occurrence will be returned.

3. Looping through the Array:

Another approach to find the index of an element in an array is to loop through the array manually and compare each element with the element you are looking for.

You can use a for loop, a forEach loop, or any other type of loop to loop through the array and compare each element with the element you are looking for.

Here’s an example using a for loop:

const array = [1, 2, 3, 4, 5];
const element = 3;
let index = -1;

for (let i = 0; i < array.length; i++) {
  if (array[i] === element) {
    index = i;
    break; // exit the loop once the element is found
  }
}

console.log(index); // Output: 2

In this example, a for loop is used to iterate through the array array. The if statement inside the loop checks if the current element at index i is equal to the element 3 that we are looking for. If it is, the index i is assigned to the index variable, and the loop is exited using the break statement.