js remove form object by key

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

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

delete person.firstname;

console.log(person.firstname);
// expected output: undefineddelete object.keyname;// Example 1
var key = "Cow";
delete thisIsObject[key]; 

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

// Example 3
delete thisIsObject.Cow;