Question

I have a mongodb function call that return a user object

User.findOne(condition, function(err, user) {
    console.log(user)   //  {username : 'blah', picture : 'blah', _id : 'blah'}
    delete user.picture;
});

somehow user object cannot be modified, delete does nothing. If I deep copy a brand new user object

var new_user = {};
for (var key in user)
    new_user[key] = user[key]

and do the deletion there, it works. Is there any situation where in Javascript when a object is not modifiable? Or did I miss something?

Answer 1

Indeed. Object properties can be made frozen, undeletable, unenumerable and not configurable. You can go check with Object.getOwnPropertyDescriptor.

console.log( Object.getOwnPropertyDescriptor( user, 'picture' ));

For instance.

If configurable is set to false, you can’t delete that property.