CODEWITHSUNDEEP
javascriptundefined
Lucas
Lucas

Reputation: 138

I want to know the difference if the value in an object in JavaScript is undefined

The variable 'bar' are all undefined. But is there any difference between obj.bar and obj2.bar?

const obj = { foo: "foo" };
console.log(obj); // { foo: 'foo' }
console.log(obj.bar); // undefined 

const obj2 = { foo: "foo", bar: undefined };
console.log(obj2); // { foo: 'foo', bar: undefined }
console.log(obj2.bar); // undefined

Upvotes: 1

Views: 43

Answers (1)

Praveen Kumar Purushothaman
Praveen Kumar Purushothaman

Reputation: 167182

In the first case, the bar is not declared. But in the second case, the bar is declared and defined to undefined.

Pretty tricky, the way to find it is, if you use Object.keys(obj), you can't find bar.

Also, using obj.hasOwnProperty('bar') will give you false. Thanks to deceze♦ for pointing it out.

const obj = { foo: "foo" };
// console.log(obj); // { foo: 'foo' }
// console.log(obj.bar); // undefined 

const obj2 = { foo: "foo", bar: undefined };
// console.log(obj2); // { foo: 'foo', bar: undefined }
// console.log(obj2.bar); // undefined

console.log(Object.keys(obj));
console.log(Object.keys(obj2));
console.log(obj.hasOwnProperty('bar'));
console.log(obj2.hasOwnProperty('bar'));

Upvotes: 3

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