1var size = Object.keys(myObj).length;

1var person={
2    "first_name":"Harry",
3    "last_name":"Potter",
4    "age":14
5};
6var personSize = Object.keys(person).length; //gets number of properties (3) 

1//length of this object is 4
2let object = {
3  'A':{
4    '10':['a','b','c']
5  }, 
6  'B':{
7    '20':['a','b','c']
8  }, 
9  'C':{
10    '30':['a','b','c']
11  }, 
12  'D':{
13    '40':['a','b','c']
14  },   
15}
16
17//Get the keys of the object (A,B,C,D) and print how many there are
18Object.keys().length
19> prints: 4
20