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JavaScript — Unset an Object Property

In some situations, you want to remove a property from a JavaScript object. This could be an in-memory cache and you want to remove a cache key from that object. Or you don’t want to store a given property when writing an object as a JSON string to the local hard disk.

This tutorial shows you how to remove a JavaScript object property.

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Removing a Key from a JavaScript Object

JavaScript comes with a delete operator. The delete operator removes a property from an object. Here’s how you would use the operator in your code:

const cache = {  
  'userId-1': { name: 'Marcus' },
}

delete cache['userId-1']  
// 'userId-1' is removed from the cache

🚨 Don’t Use JavaScript’s delete Operator

The delete operator has a drawback: dynamically deleting keys from an object can be dangerous. For example, you could unintentionally delete the hasOwnProperty key from the global Object.

Also, when deleting properties at runtime, you might use the wrong data structure. Maybe a Map suites better for a cache and JavaScript Maps come with a delete() method.

As always, you can use the delete if you know what you’re doing. It could be hard to find bugs when dynamically deleting properties from objects. That’s the reason we’re suggesting using JavaScript destructuring to unset object keys.

✅ Use JavaScript’s Destructuring to Unset an Object Property

Modern JavaScript comes with destructuring features. ECMAScript 2015 introduced destructuring and it allows you to extract properties from a JavaScript object fluently.

Here’s a sample code that you might use to remove an object key:

let cache = {  
  'userId-1': { name: 'Marcus' },
  'userId-2': { name: 'Norman' },
}

const { ['userId-1']: cacheKey, ...cacheWithoutRemovedKey } = cache

cache = cacheWithoutRemovedKey  
// 'userId-1' is removed from the `cache` object

That’s it!

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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