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JavaScript is a scripting language that can be used in both front-end and back-end development. With this programming language, you can create content that updates dynamically, animate images, and control multimedia.

JavaScript has hundreds of frameworks and libraries and is also the most-used programming language, according to Statista

JavaScript has various operators created to achieve different roles. In this article, I will explain what JavaScript Void (0) is, its importance, its use cases & benefits, potential security risks, and its alternatives. 

What is the Void (0) operator?

In our dictionaries, void means ‘not valid’ or ‘completely empty’. Void (0) is an operator that checks a given value and returns undefined. A function is considered void if it returns nothing. The void (0) operator can be used in many areas.

For instance, you can have JavaScript return undefined when you click an anchor tag. When that happens, it means that the page you are clicking will not be refreshed, and nothing will happen to that page. 

Importance of using the Void operator and 0 as an operand

You can use the void operator with any expression. However, in JavaScript, it is mostly used with 0 as its operand. Here are some use cases of the Void (0) operator:

Prevent navigation 

On normal occasions, if you click on a link, it will likely take you to a new page. We can create a project to demonstrate how it works. I will have two files on my project: index.html and nextPage.html

You can add this code to different files as follows:


<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Home Page</title>
    <h1>Welcome to the Home Page</h1>
    <a href="nextPage.html">Go to Next Page (No void operator)</a>
    <script src="script.js"></script>
<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Next Page</title>
    <h1>You are on the Next Page</h1>
    <a href="index.html">Go back to Home Page (No void operator)</a>
    <script src="script.js"></script>

Check this video out:

As you can see, you can navigate from ‘Home’ to ‘Next Page’ by clicking the button.

We can now introduce the void (0) operator that blocks navigation. Add this code to index.html:

<!-- With void operator -->
<a href="javascript:void(0);" onclick="doSomething()">Click me</a>
  function doSomething() {
    alert("Button clicked, but no navigation!");
</script><!-- With void operator -->
<a href="javascript:void(0);" onclick="doSomething()">Click me</a>
  function doSomething() {
    alert("Button clicked, but no navigation!");

Check this video out when we hit the “Click me” button:

You can see that after clicking the button, this alert, “Button clicked, but no navigation!” appears, but we don’t navigate to the next page. 

Self-Executing Anonymous Functions

A self-executing anonymous function or immediately invoked function expression (IIFE) is a function that is defined and executed after creation. Such functions are designed to create a private scope for variables that prevent these functions from polluting the global scope. 

Take a look at this code:

void function() {
    // Function to calculate the sum of numbers from 1 to n
    const calculateSum = () => {
        let sum = 0;
        for (let i = 1; i <= 10; i++) {
            sum += i;
        return sum;
    // Call the function and log the result to the console
    const result = calculateSum();
    console.log("The sum of numbers from 1 to 10 is:", result);

This is a self-executing function that adds all the numbers from 1-10 and displays the results once the code is executed. 

When you run the code, the output will be: “The sum of numbers from 1 to 10 is: 55”. 

How to Combine JavaScript and Void 0

The void operator is not exclusive to JavaScript as it is available in other programming languages like C and C++. However, the usage of this operator varies from one language to another. For instance, void is a data type in C and C++ programming languages and not an operator. 

JavaScript uses the keyword ‘void’ with the numeric zero. You can use the void () operator to prevent default behavior, such as the browser navigating to the next URL. This is a perfect example of a code block that combines JavaScript with the void () operator. 

<a href="javascript:void(0);" onclick="myFunction()">Click me</a>

You can also use the void () operator to obtain an undefined primitive value. Take a look at this code block:

const result = void(0);const result = void(0);

When you run it, you will get undefined. 

What are Void (0) benefits?

In JavaScript, we use the void () operator to create “void” or “undefined” values. These are some of the benefits of using this operator in your code:

  • Prevent navigation: We can use the void(0) Operator in the href attribute if we want to prevent the browsers from navigating to a new page when we click on a link or button. This code block illustrates how it works:
<a href="javascript:void(0);" onclick="myFunction();">Click me</a>
  • Return undefined values from functions: As a developer, you can use the void () operator to explicitly return undefined when you want code consistency in your application. Check out this code block:
function myFunction() {
    // do something
    return void(0);
  • Avoid ‘undefined’ assignment: You can use void () in such a way that ‘undefined’ is equivalent to the ‘result’. You can also use it as a stylistic choice. This code block shows how you can achieve this:
let result = void(0);
  • Make code more readable: Code readability is not something that we should ignore, especially when dealing with big applications. You can use void() when you want to explicitly discard the return value and make it known to other developers that the function will not return anything. This code block shows how you can achieve this:
function myFunction() {
  // Do something...
  return void(0);

Potential Security Risks of Void (0)

Even though void (0) is useful in various cases in JavaScript, it can also turn out to be dangerous if not used correctly. These are some of the instances where void (0) might be used maliciously:

  • Script injection vulnerabilities: There are potential risks of script injection attacks if the value passed to the void () operator is not sanitized and validated. A good example is when this value is dynamically generated based on the user input. 
<a href="javascript:void(alert('This could be malicious!'));">Click me</a>

Such a code block allows users to inject malicious code.

  • Clickjacking: Attackers can use void operators to create transparent/ invisible layers over a webpage. Such attackers will then use these layers to trick users into clicking on malicious links and buttons. 
  • Can be used to bypass Content Security Policy (CSP): Most website owners use CSP to prevent cross-site scripting (XSS) attacks. You can use CSP to restrict the nature of scripts and resources that your web pages should load. However, the use of void () operator can conflict with such measures as it loads even the scripts not allowed by the content security policy. 

Alternatives to void (0)

Technology keeps changing, and so does programming. Some people view void (0) as an outdated operator. These are some of the alternatives that modern developers use: 

  • Use event.preventDefault(): You can use event.preventDefault() to prevent the action of an event from happening. Such a statement can prevent users from submitting a form or navigating to the next page. 

These code snippets show how to use event.preventDefault:

<a href="#" onclick="event.preventDefault()">My Link</a>
document.querySelector('a').addEventListener('click', event => event.preventDefault());
  • Use # as the href value: Different pages in an application are interlinked for easy navigation. Using # as the href ensures that users remain on the same page. You can use this approach together with event.prevetDefault() to prevent your webpage from scrolling to the top. This is how you can achieve this:

<a href="#">My Link</a>
document.querySelector('a').addEventListener('click', event => {
  window.scrollTo(0, 0);
  • Use null: You can return a null value instead of undefined. This is how you can achieve this:
let result = null;


What is JavaScript?

JavaScript is a programming language mostly used in front-end development. However, this language is being used in back-end development with frameworks such as Node.js. JavaScript is mostly used with other front-end technologies like CSS and HTML to add interactivity to web pages. 

What is JavaScript Void 0?

JavaScript Void 0 is an operator that is used to prevent default action from happening. For instance, you can use void (0) to prevent navigation when a user clicks on a link or a button. When a link from a code with void (0) is clicked, the browser attempts to navigate but the results evaluate to undefined. 

Are there alternatives to void (0)?

Yes. Most modern developers use event listeners instead of void (0) in their code. This approach makes it easy to handle various functions and prevent default behavior in source codes. 

Is using void (0) safe?

You can use void (0) to prevent default behavior and with self-executing functions. However, void (0) can be dangerous if you don’t use it consciously in your code. For instance, such an operator can make it easy to inject malicious code if applied to user inputs. 


JavaScript is a very broad programming language, and you may take time before you master most of its concepts.

We have taught what the void (0) operator is its importance & use cases, and its alternatives. You also now understand how to combine JavaScript and void(0) the potential risks you are likely to come across when you use this operator. 
You may also explore some best JavaScript Runtime Environments for better code execution.

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  • Titus Kamunya
    Titus is a Software Engineer and Technical Writer. He develops web apps and writes on SaaS, React, HTML, CSS, JavaScript, Ruby and Ruby on Rails
  • Narendra Mohan Mittal

    Narendra Mohan Mittal is a versatile and experienced digital branding strategist and content editor with over 12 years of experience. He is a Gold Medalist in M-Tech and B-Tech in Computer Science & Engineering.


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