Question

How do you check if a key exists in an object in Javascript?

Answer 1

You can check whether a key exists in an object or not using three approaches,

1. Using in operator: You can use the in operator whether a key exists in an object or not

"key" in obj;

and If you want to check if a key doesn't exist, remember to use parenthesis,

!("key" in obj);

1. Using hasOwnProperty method: You can use hasOwnProperty to particularly test for properties of the object instance (and not inherited properties)

obj.hasOwnProperty("key"); // true

1. Using undefined comparison: If you access a non-existing property from an object, the result is undefined. Let’s compare the properties against undefined to determine the existence of the property.

const user = {
  name: "John",
};

console.log(user.name !== undefined); // true
console.log(user.nickName !== undefined); // false