Explain 'Not a constructor function' error in JavaScript?

The not a constructor function error occurs if we use an object or a variable as a constructor that isn’t a constructor.

Following is the code for not a constructor function error 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: 18px;
      font-weight: 500;
      color: rebeccapurple;
<h1>Not a constructor function error</h1>
<div class="result"></div>
<button class="Btn">CLICK HERE</button>
<h3>Click on the above button to use a variable as constructor</h3>
   let resEle = document.querySelector(".result");
   let BtnEle = document.querySelector(".Btn");
   let b = 22;
   BtnEle.addEventListener("click", () => {
      try {
         new b();
      catch (err) {
         resEle.innerHTML = err;


The above code will produce the following output −

On clicking the ‘CLICK HERE’ button −

Updated on: 21-Jul-2020


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