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

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