In JavaScript, the operator namely instanceof is helpful to check the object’s type at run time. It returns true if the object is an instance of a specific constructor otherwise the return value will be false.
Syntax
objectName instanceof constructorParameters
objectName: it shows the object name.
Return value
It returns the Boolean value i.e. true or false. If the object is the instance of a specific constructor true will be returned otherwise false.
Example
Let’s discuss an example to testify the type of object by using the instanceof operator in JS.
<!DOCTYPE html>
<html>
<body>
<h2 style="color:red">JS Example Code</h2>
<p id="test"></p>
<script>
var subjects= ["Maths", "Biology", "Physics"];
document.getElementById("test").innerHTML =
(subjects instanceof Object) + "<br>" +
(subjects instanceof Number) + "<br>" +
(subjects instanceof Array) + "<br>" +
(subjects instanceof String);
</script>
</body>
</html>
- Line#7: Here we have declared and initialized an array namely
"subjects". - Line#9: This part of the code checks whether the defined array is an instance of a class
Objecttype or not. - Line#10: This
(subjects instanceof Number)code checks whether the defined array is an instance of classNumber. - Line#11:
(subjects instanceof Array)checks whether the definedsubjectsis an instance of classArray. - Line#12: This part of the code checks whether the defined array is an instance of a class
String.
Output
Importance of instanceof operation in JavaScript
Variable declaration in JavaScript does not define the type of the variable. For example, we declare the variable like var x. This variable x can be a number, array, string, or user-defined data type.
In various other languages like C++, we declare the variable in a way like an int a or double b, etc. we can check that the object is related to the specific type or not by using instanceof operation in JavaScript. Thus, it is a useful operator of JavaScript.
