Use the Object.keys() method, passing the object you want to inspect, to get an array of all the (own) enumerable properties of the object.

Then calculate the length of that array by checking the length property:

const car = {
  color: 'Blue',
  brand: 'Ford',
  model: 'Fiesta'
}

Object.keys(car).length

I said enumerable properties. This means their internal enumerable flag is set to true, which is the default. Check MDN for more info on this subject.