FAQ: Iterators - The .findIndex() Method


This community-built FAQ covers the “The .findIndex() Method” exercise from the lesson “Iterators”.

Paths and Courses
This exercise can be found in the following Codecademy content:

Web Development

Introduction To JavaScript

FAQs on the exercise The .findIndex() Method

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I have a question about JavaScript.
In the code below, I noticed that the argument of the function uses the variable “animal”, as in “animal === ‘elephant’”
However, the array was declared with the function “animals” not “animal,” so how does the script “know” that animal is an item in the array “animals”
I have noticed with with a few other pieces of code, such as where an array is declared as “numbers” and later a function is passed the argument “num”. But “num” and “animal” were never declared as variables by the code. How does this work and what are the rules around it?

const animals = [‘hippo’, ‘tiger’, ‘lion’, ‘seal’, ‘cheetah’, ‘monkey’, ‘salamander’, ‘elephant’];

const foundAnimal = animals.findIndex(animal => {
return animal === ‘elephant’;


The variable is defined in the loop.

for (let animal = 0; animal < animals.length; animal++) {



Would anyone be able to explain why the ?true : false was at the end of the code?

return animal[0] === ‘l’ ? true : false;


That is a control flow device known as a ternary expression. The term refers to three components.

condition ? true case : false case
//        ^           ^
//     ternary      colon
//     operator    separator