Setters are no longer called when setting properties in object initializers: what does this mean?

Question

On this JS MDN page it says this:

JavaScript 1.8.1 note

Starting in JavaScript 1.8.1, setters are no longer called when setting properties in object and array initializers.

I just can't figure out what this is trying to tell me.

`This article is in need of a technical review.` - refer to ES5.1 spec for modern getter/setter syntax (unless you need, for some reason, to tinker with old firefox's getters/setter. And in that case, i am sorry for you) — c69, Oct 23 '12 at 22:41

score 7 · Answer 1 · answered Oct 23 '12 at 22:50

This code-snippet:

var o = {};
o.seven = 7;

and this code-snippet:

var o = { seven: 7 };

are normally equivalent; but if they're preceded by this code-snippet:

Object.prototype.__defineSetter__('seven', function(x) { alert(x); });

then only the former will alert 7 (because the setter is called by o.seven = 7, but not by o = { seven: 7 }), and only the latter will actually set o.seven to 7.

score 4 · Accepted Answer · edited May 23 '17 at 10:29

I think this refers to the issue of JSON hijacking. Have a look at

To repost my answer from this deleted question:

According to the specification, neither Array (EcmaScript 5.1 §11.1.4) nor Object literals (EcmaScript 5.1 §11.1.5) should be hijackable:

They call "the standard built-in constructor with that name", not what you might have overwritten at window.Array or window.Object

They use [[defineOwnProperty]], which does absolutely not take care of any setters on Object.prototype.

Nowadays, this should not be an issue any more in ES 5.1-compliant browsers.

Setters are no longer called when setting properties in object initializers: what does this mean?

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