即使属性存在，Node.js hasOwnProperty也不起作用

Question

In my Node.js Express application, when the user is logged in via passport the user user object is saved in the request.

It looks something like this:

{
    "uuid": "caa5cb58-ef92-4de5-a419-ef1478b05dad",
    "first_name": "Sam",
    "last_name": "Smith",
    "email": "sam@email.com",
    "password": "$2a$10$fXYBeoK6s.A8xo2Yfgx4feTLRXpdvaCykZxr7hErKaZDAVeplk.WG",
    "profile_uuid": "db172902-f3c9-456d-8814-53d07d4ea954",
    "isActive": true,
    "deactivate": false,
    "verified": true,
    "ProviderUuid": "7149f8f1-0208-41db-a78e-887e7811a169"
}

But not every user has the ProviderUuid key present. So before using its value I am trying to check if the ProviderUuid key is present in the user object

var user = req.user;
console.log('---- provider: ' + JSON.stringify(user));
console.log('--- prop: ' + user.hasOwnProperty('ProviderUuid')); //returns false
console.log('---- other method prop check: ' + Object.prototype.hasOwnProperty.call(user, "ProviderUuid")); //returns false
if('ProviderUuid' in user){
    //this returns true
}

So doing user.hasOwnProperty('ProviderUuid' ) and Object.prototype.hasOwnProperty.call(user, "ProviderUuid")) returns false, however 'ProviderUuid' in user returns true.

What am I missing here?

Answer 1

Since in works, the property must an inherited property, on one of user 's prototype objects, rather than being on user itself. Here's a live example of such behavior:

 const userProto = { foo: 'bar' }; // Create an empty object named `user` whose internal prototype is `userProto`: const user = Object.create(userProto); // False, user itself is an empty object, nothing's been assigned to it: console.log( user.hasOwnProperty('foo') ); // True, `foo` does exist on the *internal prototype* of the `user` object: console.log( 'foo' in user ); // True, `foo` is a property directly on `userProto`: console.log( userProto.hasOwnProperty('foo') ); 

So, if you want to check for the existence of an inherited property named ProviderUuid , use the in operator like you're doing.

Answer 2

I tested code and all checks returned true.

 var user = { "uuid": "caa5cb58-ef92-4de5-a419-ef1478b05dad", "first_name": "Sam", "last_name": "Smith", "email": "sam@email.com", "password": "$2a$10$fXYBeoK6s.A8xo2Yfgx4feTLRXpdvaCykZxr7hErKaZDAVeplk.WG", "profile_uuid": "db172902-f3c9-456d-8814-53d07d4ea954", "isActive": true, "deactivate": false, "verified": true, "ProviderUuid": "7149f8f1-0208-41db-a78e-887e7811a169" }; console.log('---- provider: ' + JSON.stringify(user)); console.log('--- prop: ' + user.hasOwnProperty('ProviderUuid')); //returns false console.log('---- other method prop check: ' + Object.prototype.hasOwnProperty.call(user, "ProviderUuid")); //returns false if('ProviderUuid' in user){ //this returns true } 

Try JSON.parse(), Maybe req.user saved as string