How do you check if a key exists in an Object in JavaScript?

jwdkwj8.js

let obj = { key: undefined }

// Check if the key is defined (warning: key could exist but set to undefined)
obj["key"] !== undefined;

//Check if the key is defined in the object (includes if set to undefined)
"key" in obj;

//Check if the key doesn't exist?
!("key" in obj);

//If you want to check if the key is inherited or not
obj.hasOwnProperty("key");