# Blog:JavaScript Array Methods: Every & Some

July 2018

In an earlier post, I covered the array `reduce`

method to transform array data into a new, single value. For instance, you can begin with one array of numbers that are reduced to a new set of numbers or values based on a product feature requirement.

Both array methods return a boolean value, however, there's a subtle but important distinction between

`every`

and`some`

.

This time, let's cover the `some`

and `every`

methods. Both of these methods return a `boolean`

value based on a predicate (or condition). They're pretty handy if you simply need to check an array to determine if a value or condition exists within your array's data. There's a subtle but important distinction between the two methods though, let's take a look.

`Some`

method

The `some`

method only cares **if at least one item** in an array passes the predicate (or condition). Here's an arbitrary example using the Fibonacci sequence to determine if the list includes the number `4`

:

```
const myListOfNumbers = [1, 2, 3, 5, 8, 13, 20, 33, ..., 987, ...] // ... is not a real value, used for brevity
const does4Exist = myListOfNumbers.some(num => num === 4) // Would return false
```

Since the number `4`

is clearly not in our array, our variable `does4Exist`

would be `false`

. You can change the condition `some`

evaluates on each array item to be anything else, for instance, you could check if some of the numbers in the set are even, e.g. `myListOfNumbers.some(num => num % 2)`

. In this case, we would get `true`

as a final return value using the `some`

method because there is at least one number in our sample list that is an even number.

Pro tip:for expensive calculations, like checking a large list consisting of the Fibonacci sequence, leverage memoization.

`Every`

method

The `every`

method requires every item in your array to be truthy in regard to your predicate or condition. If at least one item is falsy, `every`

will return `false`

. Using the Fibonacci sequence again, let's take a look at an example where we're wanting to know if every number in our array is even:

```
const myListOfNumbers = [1, 2, 3, 5, 8, 13, 20, 33, ..., 987, ...] // ... is not a real value, used for brevity
const isEveryNumEven = myListOfNumbers.some(num => num % 2) // Would return false
```

Our variable, `isEveryNumEven`

, would be `false`

because not every number in the Fibonacci sequence is an even number. Like the `some`

method, your predicate, or condition, can be anything else you want it to be, e.g. you could check if every number is odd, or you could compare one list to another to validate if every value in list A is in list B for instance.

I hope this helps shed some light on these two JavaScript array methods, `every`

and `some`

. Give them a try, if you're not yet too familiar with them. The MDN docs are a great resource for more information on these and other array methods, but don't hesitate to reach out if you have any questions along the way!

**Related:**

- JavaScript Array Reduce Method
- Filtering Arrays with Fat Arrows
- Asynchronous JavaScript: On Promises
- Discoverability, Semantic Markup & Accessibility
- Bias in Artificial Intelligence Confirmed
- More on JavaScript's Array Class (MDN)

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