JavaScript Basics: Object.preventExtensions and Object.isExtensible

in javascript •  7 years ago 

In JavaScript, an object is extensible by default. This means that new properties can be added to the object. In some circumstances, you my want to prevent extensions to the object. To this end, you can use Object.preventExtensions. This function prevents any extensions to the object, so that no new property can be added to the object. If you try to add new properties to the object, it will cause a TypeError (or fail silently if not in strict mode).

Here is an example:

    let myObj = {
        name: "Ali",
    };
    Object.isExtensible(myObj); // true
    Object.preventExtensions(myObj);
    Object.isExtensible(myObj); // false
    myObj.age = 19; // fails silently
    myObj.age; // undefined

It should be noted that after making an object inextensible, its __proto__ property becomes immutable. In other words, you cannot assign a new value to the __proto__ property. However, if the prototype is extensible, you can add new properties to the prototype.

As the EcmaScript standard attempts to organize the global objects, this functions are also available on the Reflect global object. So you can use Reflect.isExtensible and Reflect.preventExtensions instead.


Related Posts

Authors get paid when people like you upvote their post.
If you enjoyed what you read here, create your account today and start earning FREE STEEM!
Sort Order:  

interesting article ,, EcmaScript ! I didn't know about EcmaScript before ! can u please tell us to know what’s the difference between JavaScript and ECMAScript?? I mean in another post...actually if u have time ... regards !

Thank you. There is no difference. ECMAScript is the name of the ECMA-262 standard for the JavaScript language.

really ! thanks for the info

Great information abaout javascript....thanka for sharing..keep it up

so informative post for me. thanks for your post.

For a long time I wanted to learn JavaScript. But the schedule of the office and training was not the same at the same time. Your posts have a lot of work for me. Thanks @ghasemkiani for sharing the wonderful posts.

Bisyar khub...

Information is useful

Its great information JavaScript very good calculate but very difficult to understand . But nice lacture sir @ghasemkiani and thanks for sharing with us.
Stay blessed.
Steem on!

love to read it... thanks for sharing

Upvote done mr: @ghasemkiani

This really require more tutorial because we are in the era of technology

Javascript is onviously one of the best languages ever invented in computer world..like it

Your work is really commendable. Have a good day:)

thanx for sharing

Javascript is onviously one of the best languages ever invented in computer world.

Now a days i am looking for this type of post. Thank you sir.

nice post

great information about java program. it is useful.

useful information bro. have a nice day

Good knowledge about basic of javascript full information ..keep it sir
Thank you very much.

nice programing that is bless of technology
thanks for sharing

you create a great post....i impressed to see it...Lot of thanks for Sharing this informative and valuable post....best of luck brother....

very well post,,, Really you are giving a good post

Amazing information regarding java script. Thanks for sharing nice post. Stay blessed

javascript is a great technology in the mordern science.its basic part of one of them.i think that, its matter know should be all people.i read your post always attentively.because,new thing to know matter your basic post doing help me.thank you very much for your learning and helpful post sir..@ghasemkiani..

very well post dear @ghasemkiani
i love your post,, thanks for sharing

I appreciate your efforts to make techno post, thanks :)

Hello sir how are you...sir I need your help..plz sir follow me... i am your regular upvote and commnter..plz sir follow me

what a philosophy.... you used best article in your post.... i waiting for your next post... keep it up....

Thanks for nice post

finally seen who working on javascript on steemit... good