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JavaScript Quiz – add new key in object after freeze is possible

JavaScript Quiz – add new key in object after freeze is possible

JavaScript Object freeze –

JavaScript object freeze is used to freeze object which disallow any change in object. object freeze is difference from declaring object with const keyword.

Because const object can not be reassigned but it’s key value still can be changed.

It’s syntax look like –


For more information about javascript Object freeze click here.

JavaScript Question

In this javascript quiz code, let’s find what happen when add new key in object after object is freeze as it not allow change in key value.

First, we declare a variable detail using the let keyword and assign a javascript object to it. Which contains only the name key.

let detail = { name : “JS Startup” };

In the second step, we use a Object.freeze() method to detail variable and then change it’s name value to “JavaScript“.


detail[‘name’] = “JavaScript”;

But when we checked the value of detail name key it still the same “JS Startup”. That means, object freeze is in action.

console.log(detail.name); // output => JS Startup

Adding New Key –

In the next step, instead of changing the value of a key we added a new key active in object and assign value “true” of it.

detail[‘active’] = “true”;

Finally, let’s check the value of detail active key using console log.

console.log(detail.active); // output => ?

Any idea what should be the output of the above console log.

Answer – undefined

Click To Run Code


Now, you know the answer is undefined. But now, we not change the current value of the name key. It’s just adding new value. Let me explain

Object freeze is an important method to freeze the object. So it not only just restrict the change in the value of the key. But also not allow adding a new key in the object.

Even if you check the keys in the object after adding the active key but you will not find it.

At last, That’s why we get an answer “undefined“.

Let me know in the comment section, how to solve this also.

I hope you understand the concept and logic behind it.

But wait, i have something more for you –

Check out our other javascript quiz – 

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