how to count length of object in javascript code example

Example: length of an object in javascript

//length of this object is 4
let object = {
  'A':{
    '10':['a','b','c']
  }, 
  'B':{
    '20':['a','b','c']
  }, 
  'C':{
    '30':['a','b','c']
  }, 
  'D':{
    '40':['a','b','c']
  },   
}

//Get the keys of the object (A,B,C,D) and print how many there are
Object.keys().length
> prints: 4