this

inside

driveCar()

function refers to the global window object. Global variables

firstName

and

lastName

are added to the

window

object. That is why they are visible using the keyword

firstName = "Jack"
lastName = "Ma"

function driveCar() {
  document.write(this.firstName + ' ' + this.lastName + ' is driving a car<br/>')
}

driveCar()

If we call the same function using

call

function,

this

will refer to the object that will be passed. In this case:

john

object

let john = {
  firstName: 'John',
  lastName: 'Doe'
}

function driveCar() {
  document.write(this.firstName + ' ' + this.lastName + ' is driving a car<br/>')
}

driveCar.call(john)