Can not change object property value

Question

I am new to Javascript, I have tried this:

object1 = {};
object2 = Object.create(object1, {a:{value:1}});
object2.a = 2;

Then if I display object2.a, it is still 1 instead of 2. why is that?

Thanks.

Take a look at this post about object creation patterns and you will have a much better understanding of the difference between object1 and object2 in your example. codeproject.com/Articles/687093/… — buzzsaw
– buzzsaw, Commented Oct 13, 2015 at 1:12

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

because Object.create() is not what you think.

see this ECMAScript 5: Object creation and property definition

There are three additional aspects of a property we can control, each given a boolean value:

writable: Controls whether or not the property can be assigned. If false, attempts at assignment will fail. Only applies to data descriptors.

enumerable: Controls whether or not this property will appear in for...in loops.

configurable: Controls whether or not the property can be deleted, and whether its property descriptor (other than writable) can be changed.

Each of these defaults to false if not supplied.

so what you need is :

var object1 = {};
var object2 = Object.create(object1, {
    a: {
        value: 1,
        writable: true
    },
});
object2.a = 2;

Have fun : )

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Oct 13, 2015 at 1:24

Far east

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3 Comments

totally Over a year ago

Thanks. There is a sentence in the article "writable: Controls whether or not the property can be assigned. If true, attempts at assignment will fail. Only applies to data descriptors." I am confused by it, it said, if true, assignment will fail. but default is false, means assignment will be ok?. is there something wrong with that sentence? should "if true" be "if false"?

Bergi Over a year ago

@totally: Indeed, that logic is messed up

Far east Over a year ago

@totally that's a mistake , sorry for that ; p

Hussam · Accepted Answer · 2015-10-13 01:31:57Z

1

try this:

var object1 = {};
var object2 = Object.create(object1, {a:{value:1,writable: true}});
object2.a = 2;

see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperties

edited Oct 13, 2015 at 1:31

answered Oct 13, 2015 at 1:10

Hussam

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