tipos de datos Objets en javascript

Objetos

> var o1= {};
undefined
> var user ={first_name:"cesar", last-name:"morones"};
...
> var user ={first_name:"cesar", last_name:"morones"};
undefined
> user
{ first_name: 'cesar',
  last_name: 'morones' }
> user.cumpleaños = "11 d ejulio"
'11 d ejulio'
> user
{ first_name: 'cesar',
  last_name: 'morones',
  'cumpleaños': '11 d ejulio' }
> user.cumpleaños
'11 d ejulio'
> user.favorite_drink
undefined
> user
{ first_name: 'cesar',
  last_name: 'morones',
  'cumpleaños': '11 d ejulio' }

> delete user.cumpleaños
true
> user
{ first_name: 'cesar',
  last_name: 'morones' }

> user["fruit"] = "bananna"
'bananna'
> user
{ first_name: 'cesar',
  last_name: 'morones',
  fruit: 'bananna' }



> Object.keys(user)
[ 'first_name',
  'last_name',
  'fruit' ]
> Object.keys(user).length
3