The ECMAScript language specification defines the [[writable]] attribute of Object.defineProperty() as following:
However, this definition doesn't make any sense. There it says that if [[writable]] is false, any attempts to use [[set]] will not work. So in other words: if [[writable]] is false then we can't change it to an accessor property of a setter.
However, in the example below we have an object where we are able to define [[set]] despite [[writable]] being false:
var plainObj = new Object();
Object.defineProperty(plainObj, "v1", {
configurable: true,
writable: false, //<---- attribute [[writable]] is 'false'
value: "handsome-and-SKINNY"
});
//setting an [[set]] attribute:
Object.defineProperty(plainObj, "v1", {
set: function (input) {
console.log("Setter's value: " + input);
}
});
//passing argument to setter
plainObj.v1 = "passed argument";
Console output:
Setter's value: passing argument
So as you can see, we have successfully defined an [[set]] attribute and passed in some arguments into it, despite the fact that it shoudn't be happening because [[writable]] was set to false. Any explenations are appreciated.
writable: false means that value: "handsome-and-SKINNY" is constant:
Object.defineProperty(plainObj, "v1", {
configurable: true,
writable: false, // hhh can't be changed
value: "hhh"
});
plainObj.v1 = "aaa"
console.log(plainObj.v1)
hhh
Object.defineProperty(plainObj, "v1", {
configurable: true,
writable: true, // hhh can be changed
value: "hhh"
});
plainObj.v1 = "aaa"
console.log(plainObj.v1)
aaa
Property may be redefined even if value is not writable
writable
true if the value associated with the property may be changed with an assignment operator. Defaults to false.
If false, attempts by ECMAScript code to change the property's [[Value]] attribute using [[Set]] will not succeed.
However, this definition doesn't make any sense. There it says that if [[writable]] is false, any attempts to use [[set]] will not work.
You misunderstood the specification.
When the property is a data property, it is defined by the [[Value]] and [[Writable]] attributes, [[Get]] and [[Set]] are not present. When the property is an accessor property, it is defined by the [[Get]] and [[Set]] attributes, [[Value]] and [[Writable]] are not present.
The phrase "change the property's [[Value]] attribute using [[Set]] will not succeed." does not refer to the [[Set]] attribute of a data property descriptor record, it refers to the [[Set]]() internal object method which will not succeed.
Your example code did change the data property into an accessor property, thereby also removing the [[Writable]] attribute. It now can be written to as long as there is a setter.