JavaScript instanceof Operator

JavaScript instanceof operator will find the object type at the time of runtime. The outcome we can expect can be Boolean values that are either true or false which are based on the inputs we gave and the objects that are included.

Syntax:

Parameters

ObjectName: The name of the object.

ObjectType: It determines the object's type which is used for testing.

Why is an instanceof necessary in JavaScript?

Instanceof operator in JavaScript is necessary due to when we declare XYZ as a variable that represents many user-defined datatypes it can be used for many purposes like integers, characters, arrays, and many other datatypes. So, this operator will help us to identify the particular datatype for which an object is linked.

Example 1: The Instanceof Operator and Inheritance

We will discuss some of the examples related to instanceof operator here:

Code

Output

Justification

1. Initially, a course array containing a few course values was created.
2. Next, we verified that the object of the course was an instance of the array type; since courses are an array type, we were provided with the true value.
3. After that, we verified that the object of the course was an instance of the Number type; since courses are not a Number type, the result was false.

Example 2: Symbol.hasInstance

Just like how we can employ the instanceof operator to ascertain if an object is a class instance, we can use Symbol.hasInstance to check if a class includes an object instance. Symbol.hasInstance will return true if an object exists in the class; otherwise, it will return false.

Code

Output

Justification

1. We started by creating a class called Lang and adding a constructor to it.
2. Next, we made an object called Java and set its initial state to be the class Lang instance.
3. Lastly, we have used the Symbol.hasInstance method to determine whether or not the class Lang contains an instance of the object Java.

Example 3: Making use of String with instanceof

We'll see how the instanceof operator handles String objects in this example.

Code

Output

Justification

1. We started a sentence in the first step by initializing it with "Today is Monday."
2. Next, a string object was made.
3. Ultimately, we have verified which object belongs to which class.

Example 4: Making use of Date and instanceof

We will examine the behavior of the instanceof operator when working with Date objects in this example.

Code

Output

Justification

1. We created an object of the Date class in the first step and gave it the name new_date.
2. Lastly, we have verified which class the object is an instance of.

Example 5: Using Object.create() to Create Objects

We will examine the behavior of the instanceof operator in this example when we use the Object.create() method to create the object.

Code

Output

Example 6: Not an instanceof

In this example, we will learn how to check whether an object is an instance of a class or not by using the Not operator in conjunction with the instanceof operator.

Code

Output

Justification

1. Two functions, Class1() and Class2(), were created in the first step and are both empty.
2. Next, we made an object called obj and assigned it to be a Class2() instance.
3. Next, we ascertained which object belongs to which class.
4. Next, by applying the (!) inside the if condition, we have utilized the not an instanceof method by placing a not (!) operator in front of the instanceof method, we can make the object an instance of Class1() if the condition is met.

In summary

From the article, we learned the following:

1. To determine an object's type at runtime, use the JavaScript instanceof operator.
2. If the object is an instance of a specific class, the JavaScript instanceof operator will return true; otherwise, it will return false.
3. ObjectName and ObjectType are the two parameters that the JavaScript instanceof operator takes as arguments.
4. If the ObjectType is not an object, the JavaScript instanceof operator will throw an exception.