Delete operation in Javascript

Question

I am having trouble understanding delete operation in javascript.

I have an object like follows -

var object = {"name" : "abc"};

object.prototype = {"name" : "xyz"};

If I delete the "name" property from object it should delete it from the object and not from the prototype as the prototype values are only used in get operation.

So after -

delete object.name

If I print object.name it gives me 'undefined', while in my opinion it should give me 'xyz'.

First i thought that the delete operation is just setting the value of object.name to 'undefined', but then object.hasOwnProperty('name') gives me false.

Am I missing anything?

If I print object.name it gives me 'undefined', while in my opinion it should give me 'xyz'. It seems that you confuse object.name and object.prototype.name — hindmost
– hindmost, Commented Mar 23, 2016 at 10:36
The behavior you describe would occur only if the prototype occurs in the prototype chain. — RamblinRose
– RamblinRose, Commented Mar 23, 2016 at 10:40

Quentin · Accepted Answer · 2016-03-23 10:39:15Z

7

The hole in your understanding is with prototypes, not delete.

Values on the prototype appear on instances of an object, not the object to which the prototype property belongs.

You need to create a constructor function, put the prototype on that, then instantiate an object from that function using new.

function MyObject (name) {
  this.name = name;
}

MyObject.prototype.name = "xyz";

var instance = new MyObject("abc");

document.write(instance.name);
document.write("<br>");
delete instance.name;
document.write(instance.name);

answered Mar 23, 2016 at 10:39

Quentin

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2 Comments

Will Jenkins Over a year ago

Great answer but I'm struggling with "Values on the prototype appear on instances of an object, not the object to which the prototype property belongs" - can anyone expand a little, please?

Quentin Over a year ago

@WillJenkins — Umm. I did. In the next paragraph.

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