javascript remove object key

let person = {
  firstname: 'John',
  lastname: 'Doe'
}

console.log(person.firstname);
// expected output: "John"

delete person.firstname;

console.log(person.firstname);
// expected output: undefined

var person = {"first_name": "Billy","last_name": "Johnson"};
delete person.last_name; //delete last_name property

var obj = {a: 5, b: 3};
delete obj["a"];
console.log(obj); // {b: 3}

delete object.keyname;

delete obj.firstname;

// Example 1
var key = "Cow";
delete thisIsObject[key]; 

// Example 2
delete thisIsObject["Cow"];

// Example 3
delete thisIsObject.Cow;