Question

138

when do you use Object.defineProperty()

rated 0 times [ 144] [ 6] / answers: 1 / hits: 19298 / 12 Years ago, wed, april 11, 2012, 12:00:00

I'm wondering when I should use

Object.defineProperty

to create new properties for an object. I'm aware that I'm able to set things like

enumerable: false

but when do you need this really? If you just set a property like

myObject.myprop = 5;

its descriptors are all set to true, right? I'm actually more curious when you guys use that rather verbose call to .defineProperty() and for what reasons.

Answers

Only authorized users can answer the question. Please sign in first, or register a free account.

carolynt

Add To Favorites

Follow

Total Points: 252

Total Questions: 98

Total Answers: 109

Location: French Southern and Antarctic Lands

Member since Sat, Oct 31, 2020

4 Years ago

answered 12 Years ago jordenfabiand · Accepted Answer

Object.defineProperty is mainly used to set properties with specific property descriptors (e.g. read-only (constants), enumerability (to not show a property in a for (.. in ..) loop, getters, setters).

use strict;

var myObj = {}; // Create object

// Set property (+descriptor)

Object.defineProperty(myObj, 'myprop', {

    value: 5,

    writable: false

});

console.log(myObj.myprop);// 5

myObj.myprop = 1;         // In strict mode: TypeError: myObj.myprop is read-only

Example

This method extends the Object prototype with a property. Only the getter is defined, and the enumerability is set to false.

Object.defineProperty(Object.prototype, '__CLASS__', {

    get: function() {

        return Object.prototype.toString.call(this);

    },

    enumerable: false // = Default

});

Object.keys({});           // []

console.log([].__CLASS__); // [object Array]