Getting and Setting Property Descriptors in JavaScript (Part 1)

In this post, I am going to tell you how you can get the property descriptor for a specific property in a JavaScript object. As I said in my previous post, property descriptors can be obtained with the help of two functions on the Object constructor, viz. Object.getOwnPropertyDescriptor and Object.getOwnPropertyDescriptors functions.

First let's set the stage by creating a simple object with two properties:

    let ali = {
        age: 19,
        get name() {
            if (typeof this._name === "undefined") {
                this._name = "Ali";
            }
            return this._name;
        },
        set name(name) {
            this._name = name;
        },
    };

Here, age is a data property and name is an accessor property. Let's get the descriptor for the first property:

    Object.getOwnPropertyDescriptor(ali, "age");

This gives us the following result:

    {
        value: 19,
        writable: true,
        enumerable: true,
        configurable: true,
    }

For the name property, we get the following descriptor:

    {
        get: function () {
            if (typeof this._name === "undefined") {
                this._name = "Ali";
            }
            return this._name;
        },
        set: function (name) {
            this._name = name;
        },
        enumerable: true,
        configurable: true,
    }

As you can see, attributes value and writable are only used for data properties. On the other hand, attributes get and set are obviously used only for accessor properties.

Now, what about the Object.getOwnPropertyDescriptors function? This one gives you an object with all own property descriptors of the object. In other words, the resulting object maps property names to property descriptors. We can call this function like this:

    Object.getOwnPropertyDescriptors(ali);

This gives us the following result:

    {
        age: {
            value: 19,
            writable: true,
            enumerable: true,
            configurable: true,
        },
        name: {
            get: function () {
                if (typeof this._name === "undefined") {
                    this._name = "Ali";
                }
                return this._name;
            },
            set: function (name) {
                this._name = name;
            },
            enumerable: true,
            configurable: true
        },
    }

As you can see, value and writable attributes are only used in data properties, and get and set attributes are only used for accessor properties.

In the next post, I am going to write about setting property descriptors.

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Related Posts

• Object Creation and Manipulation Functions in JavaScript
• Property Descriptors in JavaScript