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  3. Check If an Array Contains a Given Value in JavaScript or Node.js

Check If an Array Contains a Given Value in JavaScript or Node.js

When working with arrays in JavaScript, a typical task is to determine whether a given values exists in the array. For example, you may want to ensure that a list of objects contains only items with unique names.

This tutorial shows you how to determine whether a JavaScript array includes a given value.

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Check If an Array Contains a Given Value

A typical setup in your app is a list of objects. Here, we’re using an array of users. The task is to check if a user with a given name exists in the list of users.

You can check if the users array contains a given value by using the array.find(predicate) method. This method returns the first item matching the predicate function. If none of the items matches the predicate, it returns null.

In combination with two negation operators !! you’ll receive a boolean value. Here’s a code sample showing you how to check if an array of users contains a given user:

const users = [  
  { id: 1, name: 'Marcus' },
  { id: 2, name: 'Norman' },
  { id: 3, name: 'Christian' }
]

const containsMarcus = !!users.find(user => {  
  return user.name === 'Marcus'
})
// true

const containsFutureStudio = !!users.find(user => {  
  return user.name === 'Future Studio'
})
// false

There’s another way to check whether a JavaScript array includes a specific value: the array.includes method.

The downside of array.includes(value) is that you can only provide a dedicated value. This approach doesn’t work reliably with objects. The comparison is only true if strict equality (===) exists.

In contrast to object comparisons, the array.includes() method works reliably with primitive values, like strings and numbers:

const names = ['Marcus', 'Norman', 'Christian']

const containsMarcus = names.includes('Marcus')  
// true

const containsMarcus = names.includes('Future Studio')  
// false

Depending on the array you’re running the check on, you may choose one of the array methods array.find(predicate) or array.includes(value) to detect whether a specific value exists.

Make Your Code More Readable by Using a Package

I’m the maintainer of the @supercharge/collections package providing convenient array methods.

The package provides a fluent interface interacting with a given array. One of the methods allows you to check whether the given array has a specific item.

Use the collection.has(predicate) method in combination with a predicate function determining whether the collection contains a given value:

const Collect = require('@supercharge/collections')

const users = [  
  { id: 1, name: 'Marcus' },
  { id: 2, name: 'Norman' },
  { id: 3, name: 'Christian' }
]

Collect(users).has(user => {  
  return user.name === 'Marcus'
})
// true

The collection.has() method reads more intuitively. It requires less mental energy when reading the code in contrast to !!array.find().

Mentioned Resources

Marcus Pöhls

Marcus is a fullstack JS developer. He’s passionate about the hapi framework for Node.js and loves to build web apps and APIs. Creator of Futureflix and the “learn hapi” learning path.

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