Difference Between indexOf and findIndex function of array

The task is to differentiate between the indexOf() and findIndex() methods of JavaScript. we're going to discuss both approaches.

JavaScript indexOf() Method: This method is used to find the index of the first occurrence of the elements provided for search as the argument to the function. 

Syntax: 

arr.indexOf(element[, index])

Parameters: 

• element: This parameter specifies the element to be searched.
• index: This parameter specifies from which index search to start.

Return value: This method returns the index of the string (0-based) where the search value is found for the first time. If the search value cannot be found in the string then the function returns -1.

JavaScript findIndex() Method: This method returns the index of the first element of the given array which satisfies the testing function. 

Syntax: 

array.findIndex(fun(curValue, index, arr), thisValue)

Parameters: 

• fun: This parameter specifies a function to be run for every element of the array.
• curValue: This parameter specifies the value of the current element.
• index: This parameter specifies the array index of the current element.
• arr: This parameter specifies the array object with the current element belongs.
• thisValue: This parameter specifies a value to be passed to the function to be used as its “this” value. If this is empty, the value “undefined” will be used.

Return value: It returns the array element index if any of the elements in the array pass the test, otherwise, it returns -1.

Example 1: In this example, indexOf() method is used. 

let array = ["Geeks", "GFG", "geeks", "Geeks"];

console.log("Array: [" + array + "]");

console.log("First index of 'Geeks' is " 
    + array.indexOf('Geeks'));

Array: [Geeks,GFG,geeks,Geeks]
First index of 'Geeks' is 0

Example 2: In this example, findIndex() function is used. 

let array = [1, 3, 4, 5, 6, 7, 8, 9];

console.log("Array: [" + array + "]");

function getEven(n) {
    if (n % 2 == 0) {
        return 1;
    }
    return 0;
}

console.log("First even number in array is at index "
        + array.findIndex(getEven));

Array: [1,3,4,5,6,7,8,9]
First even number in array is at index 2

Conclusion:

• The indexOf() method is used when we want to find the first occurrence of a specified element and the element is known.
• The findIndex() method is used when we want to specify a particular condition to that element. 
• JavaScript indexOf() method takes direct element is specified so it is useful when we are working with array of objects.
• JavaScript findIndex() method takes a callback function which returns the value of the element whose index is to be found.