findIndex.js

'use strict'

// Starting array
const ages = [7, 24, 21, 18, 22]

// Use indexOf to find the position of 21
ages.indexOf(21) // 2

// Use findIndex to find the position of first age over 21
// using a predicate function
const isAdult = (age) => {
  return age >= 21
}
ages.findIndex(isAdult) // 1