delete 操作符用于删除对象的某个属性;如果没有指向这个属性的引用,那它最终会被释放。
const Employee = {
firstname: 'John',
lastname: 'Doe'
}
console.log(Employee.firstname);
// expected output: "John"
delete Employee.firstname;
console.log(Employee.firstname);
// expected output: undefined