The in JavaScript

The is a metaproperty that allows us to determine at runtime whether a function or constructor was called using the new keyword or not.

Following is the code for in JavaScript −


 Live Demo

<!DOCTYPE html>
<html lang="en">
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
   body {
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
   .result {
      font-size: 20px;
      font-weight: 500;
      color: blueviolet;
<h1> in JavaScript.</h1>
<div class="result"></div>
<br />
<button class="Btn">CLICK HERE</button>
<h3>Click on the above button to call the Student constructor without the new keyword</h3>
   let resEle = document.querySelector(".result");
   let BtnEle = document.querySelector(".Btn");
   function Student(name, age, place) {
      if (! {
         resEle.innerHTML ="Error : Student should be used with the new operator";
      } = name;
      this.age = age; = place;
   BtnEle.addEventListener("click", () => {
      Student("Shawn", 22, "Delhi");


On clicking the ‘CLICK HERE’ button −

Updated on: 20-Jul-2020


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