Learn
Iterators
The .findIndex() Method

We sometimes want to find the location of an element in an array. That’s where the `.findIndex()` method comes in! Calling `.findIndex()` on an array will return the index of the first element that evaluates to `true` in the callback function.

``````const jumbledNums = [123, 25, 78, 5, 9];

const lessThanTen = jumbledNums.findIndex(num => {
return num < 10;
});``````
• `jumbledNums` is an array that contains elements that are numbers.
• `const lessThanTen =` declares a new variable that stores the returned index number from invoking `.findIndex()`.
• The callback function is an arrow function has a single parameter, `num`. Each element in the `jumbledNums` array will be passed to this function as an argument.
• `num < 10;` is the condition that elements are checked against. `.findIndex()` will return the index of the first element which evaluates to `true` for that condition.

Let’s take a look at what `lessThanTen` evaluates to:

``console.log(lessThanTen); // Output: 3 ``

If we check what element has index of 3:

``console.log(jumbledNums); // Output: 5``

Great, the element in index `3` is the number `5`. This makes sense since `5` is the first element that is less than 10.

If there isn’t a single element in the array that satisfies the condition in the callback, then `.findIndex()` will return `-1`.

``````const greaterThan1000 = jumbledNums.findIndex(num => {
return num > 1000;
});

console.log(greaterThan1000); // Output: -1``````

### Instructions

1.

Invoke `.findIndex()` on the `animals` array to find the index of the element that has the value `'elephant'` and save the returned value to a `const` variable named `foundAnimal`.

2.

Let’s see if we can find the index of the first animal that starts with the letter `'s'`.

Call `.findIndex()` on the animals array return the index of the first element that starts with `'s'`. Assign the returned value to a `const` variable named `startsWithS`.