JavaScript Objects: Properties, Methods, and Accessors

Introduction to JavaScript Objects

	JavaScript is an object-oriented programming language, so everything in JavaScript is an object.
	A JavaScript object is like a real-world entity having state and behavior, for example, a car. We can take a car as an object. It will have a state like color and model. It will also have behaviors like accelerating and brake.
	JavaScript is template based and we can create objects without the need of having a class. Generally, an object is accompanied by a class that defines an object’s blueprints but JavaScript doesn’t require any class to be defined for objects

Create a JavaScript Object

There are three ways in which we can create a JavaScript object. Let’s go through each method:

• We can use the object literal to create and define a JavaScript object. In this method, an object can be created in a way very similar to that of defining a dictionary, with keys and associated values. 
• In this case, one of the keys can be age and its value is 21.

<script>

      var student = {

        name: "Chris Hemsworth",

        age: 21,

        branch: "Computer Science",

      };

      document.getElementById("demo").innerHTML = student.name + " of the age " + student.age + " studies " + student.branch + ".";

    </script>

• We can use the new keyword to create and define an object. This method is similar to how objects are created in the Java programming language. We can easily add properties to JavaScript objects too like illustrated below. 

<script>

      var student = new Object();

      student.name = "Chris Hemsworth";

      student.age = 21;

      student.branch = "Computer Science";

      document.getElementById("demo").innerHTML = student.name + " of the age " + student.age + " studies " + student.branch + ".";

    </script>

• We can also use an object constructor to initialize a JavaScript object. This method is also commonly known as object prototyping. The constructor takes in a few parameters and using those parameters, we define the value for each property in an object.

    <script>

      function stud(name, age, branch) {

        this.name = name;

        this.age = age;

        this.branch = branch;

      }

      var student = stud("Chris Hemsworth", 21, "Computer Science");

      document.getElementById("demo").innerHTML = student.name + " of the age " + student.age + " studies " + student.branch + ".";

    </script>

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JavaScript Object Properties

A JavaScript object is basically a collection of unordered properties. Values associated with a JavaScript object are called its properties. Properties can usually be added, updated, and deleted, excluding read-only properties.

Let’s now look at the few ways for accessing object properties:

<!--ways to access properties of objects-->

    <script>

      var student = {

        name: "Chris Hemsworth",

        age: 21,

        branch: "Computer Science",

      };

      //first method

      student.age;

      //second method

      student[age];

      //third method

      x = "age";

      student[x];

    </script>

• We first define an object and name it student and add a few relevant properties.
• The first method is to access the property by using the dot(.) notation - object.property
• The second method is by using square brackets - object[property]
• Lastly, we can store a property name, in the form of a string, in a variable and then use that variable to access the associated property.

JavaScript Object Methods

Actions that can be performed on a JavaScript object are called methods.

<script>

      let user = {

        name: "Chris",

        age: 24,

      };

      // create a new function that we will use as an object method

      function sayHi() {

        alert("Hello!");

      }

      // then add the previously created method

      user.sayHi = sayHi;

      // this will print username on the screen

      document.getElementById("demo").innerHTML = "Hi " + user.name;

      //user.sayHi(); // this will create an alert, Hello!

      document.getElementById("click me").onclick = user.sayHi;

    </script>

• We first define an object, user; and add a couple of properties to it, namely, name and age.
• Then we create a new function that throws an alert saying “Hello!”.
• We can add this method to the object the same way we add properties to objects.
• We then use JavaScript DOM to attach an event listener to an HTML button that in turn triggers the alert when clicked on.

JavaScript Object Accessors

Getters and setters allow the defining of object accessors.

<!--JavaScript getter-->

    <script>

      // Create an object:

      var car = {

        model: "BMW 320d",

        color: "Navy Blue",

        fuel_type: "Diesel",

        get fuel() {

          return this.fuel_type;

        },

      };

      // Display data from the object using a getter:

      document.getElementById("demo").innerHTML = car.fuel;

    </script>

    <script>

      var car = {

        model: "Audi A4",

        color: "Bright Red",

        fuel_type: "",

        set fuel(fuel) {

          this.fuel_type = fuel;

        },

      };

      // Set an object property using a setter:

      car.fuel = "Petrol";

      // Display data from the object:

      document.getElementById("demo").innerHTML = car.fuel_type;

    </script>

• We first create an object, car, and add a few properties to that object.
• Then, we can use a getter() function to access the properties of an object, this helps in the implementation of abstraction in a JavaScript application.
• We can also set the value of a property of an object using setter() function, this provides more control as to what values can be assigned to that particular property.

I hope you are now familiar with JavaScript objects and excited enough to start learning more about it right away!

Objects are a crucial part of any Object-oriented programming language. So it is important to know the ins and outs of this concept properly. Taking the time to learn about JavaScript objects will help you in getting ready for real-world applications and for the interviews as well.

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