let user = {};
for(key in user) alert(key, user[key]);
user["name"] = "John"
for(key in user) alert(key, user[key]);
user["surname"] = "Smith"
for(key in user) alert(key, user[key]);
user["name"] = "Pete"
for(key in user) alert(key, user[key]);
delete user["name"];
for(key in user) alert(key, user[key]);