In JavaScript, there are numerous methods used to manage an object by accessing, changing, or returning properties.

The Object.defineProperty() method can be used to:

• Add a new property to an object
• Change property values
• Change property metadata
• Change object getters and setters

Syntax:

Object.defineProperty(object, property, descriptor)

Adding a new property:

// create target object
const person = {
    firstName: "Johnny",
    lastName: "Shay",
    age: 12
};

// add a property
Object.defineProperty(person, "year", {value:"2013"}); // adds the property year which equals 2013

Changing a property value:

// create target object
const person = {
    firstName: "Johnny",
    lastName: "Shay",
    age: 12
};

// add a property
Object.defineProperty(person, "firstName", {value : "Marty"}); // changes the property firstName to Marty

All properties have a name and value, and can have attributes such as enumerable, configurable, and writable.

Setting an attribute to true:

• writable : true // property value can be changed
• enumerable : true // property can be enumerated
• configurable : true // property can be reconfigured

Setting an attribute to false:

• writable : false // property value can not be changed
• enumerable : false // property can be not enumerated
• configurable : false // property can be not reconfigured

// create target object
const person = {
    firstName: "Johnny",
    lastName: "Shay",
    age: 12
};

// make age read only
Object.defineProperty(person, "age", {writable:false});

The Object.getOwnPropertyNames() method can list object properties.

Syntax:

Object.defineProperty(object, property, descriptor)

List all object properties:

// create target object
const person = {
    firstName: "Johnny",
    lastName: "Shay",
    age: 12
};

// get all properties
Object.getOwnPropertyNames(person); // firstName,lastName,age

The Object.keys() method can list enumerable object properties.

Syntax:

Object.keys(object)

List all object properties:

// create target object
const person = {
    firstName: "Johnny",
    lastName: "Shay",
    age: 12
};

// get all properties
Object.getOwnPropertyNames(person); // firstName,lastName,age

The Object.defineProperty() method can be used to add Getters and Setters to an Object.

// create target object
const person = {
    firstName: "Johnny",
    lastName: "Shay",
    age: 12
};

// Define a getter
Object.defineProperty(person, "fullName", {
    get: function () {return this.firstName + " " + this.lastName;}
});

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