when do you use Object.defineProperty()

ecmascript-5, javascript

Solution

`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]"

Problem

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.

Original source