Difference Between indexOf and findIndex function of array

Question

I am confused between the difference between the two function indexOf and find Index in an array.

The documentation says

findIndex - Returns

Answer 1

The main difference are the parameters of these functions:

-> Array.prototype.indexOf() :

   var fruits = ["Banana", "Orange", "Apple", "Mango"];
   var a = fruits.indexOf("Apple");
   The result of a will be: 2

->Array.prototype.findIndex() :

       var ages = [3, 10, 18, 20];

       function checkAdult(age) {
        return age >= 18;
       }

       function myFunction() {
         document.getElementById("demo").innerHTML = 
         ages.findIndex(checkAdult);
       }

       The result will be: 2