How to Check a Key Exists in JavaScript Object?

2. Using hasOwnProperty() Method

The hasOwnProperty() method is another way to verify if a key exists. It checks if the key is directly in the object, excluding any inherited properties.

Syntax

object.hasOwnProperty("key")

Example

const person = {
    firstName: "Alice",
    lastName: "Doe",
    age: 25
};

console.log(person.hasOwnProperty("firstName")); 
console.log(person.hasOwnProperty("gender"));   

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Output

true
false

Explanation:

• The method returns true for firstName as it is a property of person.
   
• It returns false for gender because the key is not present.

3. Using Object.keys() Method

The Object.keys() method returns an array of a given object's own property names. You can use the includes() method to check if a key exists in this array.

Syntax

Object.keys(object).includes("key")

Example

const car = {
    brand: "Toyota",
    model: "Corolla",
    year: 2022
};
console.log(Object.keys(car).includes("model"));  
console.log(Object.keys(car).includes("color")); 

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Output

true
false

Explanation:

• Object.keys(car) returns ["brand", "model", "year"].
   
• includes("model") returns true, indicating that model exists.
   
• includes("color") returns false as color is not a key.

Frequently Asked Questions

What is the best method to check if a key exists in an object?

The hasOwnProperty() method is the best choice when you want to check only the object's own properties, while the in operator includes inherited properties.

Can an object have a key with an undefined value?

Yes, an object can have a key with an undefined value. The in operator will still return true for such keys.

How do I check for a nested key in a JavaScript object?

You can use optional chaining like object?.key?.nestedKey to safely check for nested keys without errors.

Conclusion

In this article, we discussed different ways to check if a key exists in a JavaScript object. We discussed methods like the in operator, hasOwnProperty(), and Object.hasOwn(), each with its specific use case. Understanding these techniques helps developers write more reliable and efficient code when working with JavaScript objects.