instanceof operator in JavaScript
The instanceof operator is used to check the type of an object at run time. Every object in JavaScript has a prototype, accessible through the __proto__ property . Functions also have a prototype property, which is the initial __proto__ for any objects created by them. When a function is created, it is given a unique object for prototype. The instanceof uses the prototype of an object to determine if it's an instance of a class or a constructed function. It returns a boolean value that indicates if an object is an instance of a particular class.
const Animal = function(type) {
this.type = type;
}
const dog = new Animal('dog');
document.write(dog instanceof Animal); //returns true
document.write(dog instanceof Object); //returns true
Which is best to use: instanceof or typeof?
Both are similar in functionality because they both return type information, however, it is better to prefer instanceof because it's comparing actual types rather than strings. Type comparison is less prone to human error, and it's technically faster since it's comparing pointers in memory rather than doing whole string comparisons.
Related Topics
- JavaScript Interview Questions (Part2)
- JavaScript Interview Questions (Part3)
- Is JavaScript a true OOP language?
- Advantages and Disadvantages of JavaScript
- Difference Between JavaScript and ECMAScript?
- What is noscript tag?
- Escaping Special Characters in JavaScript
- What is undefined x 1 in JavaScript?
- JavaScript : Logical Operators
- Difference between '=', '==' and '===' operators?
- How to reload a page using JavaScript?
- How to write html code dynamically using JavaScript?
- How to add html elements dynamically with JavaScript?
- How to load another html page from javascript?
- What Is The Disadvantages Using InnerHTML In JavaScript?
- What is Browser Object Model
- How to detect the OS on the client machine in JavaScript?
- Difference between window, document, and screen in Javascript?
- Difference between the substr() and substring() in JavaScript?
- How to replace all occurrences of a string in JavaScript?
- How to test a string as a literal and as an object ?
- What is Associative Array? How do we use it?
- What is an anonymous function in JavaScript?
- What is the use of 'bind' method in JavaScript?
- Pure functions Vs. Impure functions in javascript
- Is Javascript a Functional Programming Language?
- What's the Difference Between Class and Prototypal Inheritance?
- Javascript, Pass by Value or Pass by Reference?
- How to prevent modification of an object in Javascript?
- What is 'this' keyword in JavaScript?
- How Does Function Hoisting Work in JavaScript?
- What do mean by NULL in Javascript?
- What does the delete operator do in JavaScript?
- What is the Infinity property used for in Javascript?
- Event bubbling and Event Capturing in JavScript?
- What is "strict mode" and how is it used in JavaScript?
- What is the difference between .call() and .apply()?
- Entire content of a JavaScript source file in a function block?
- What is an immediately-invoked function expression?
- What is escape & unescape String functions in JavaScript?
- What Are RESTful (REpresentational State Transfer)Web Services?
- What is Unobtrusive JavaScript & Why it's Important?
- What Does JavaScript Void(0) Mean?
- What are JavaScript Cookies?
- Difference between Client side JavaScript and Server side JavaScript
- TypeError: document.getelementbyid(...) is null
- Uncaught TypeError: Cannot read property of undefined In JavaScript
- What's the difference between Null and Undefined?