What is void(0) in JavaScript

What is void(0) in JavaScript

Welcome to codedamn, where we thrive on demystifying technical concepts and making them accessible to all. Today, we will be dissecting and understanding a particularly curious element in JavaScript that might have left you scratching your head: void(0). To some, it might appear as an enigmatic piece of code, to others, it's a common technique used in JavaScript programming. Either way, it's essential knowledge for anyone looking to deepen their understanding of JavaScript.

What is void(0)?

The void operator in JavaScript is an interesting, yet lesser-known, part of the JavaScript arsenal. Its primary purpose is to evaluate an expression and then return undefined. Basically, it's a way of obtaining the undefined primitive value. The syntax for using void is as follows:


The expression is a JavaScript expression to evaluate. After evaluation, void discards the expression's return value and returns undefined. It's the "(0)" part that often confuses developers. Technically, you can pass anything to the void operator, not just zero. So void(0), void(1), void('hello'), void(function(){}) all return undefined.

Why Use void(0)?

So, why would any developer want to use void(0) in their code? One of the main reasons to use void(0) is to prevent the page from refreshing, especially when using anchor tags <a>. In JavaScript-enabled browsers, <a href="javascript:void(0)"> prevents the default action of clicking a hyperlink, which is navigating to a new URL.

For example:

<a href="javascript:void(0)" onclick="showPopup();return false;">Show Popup</a>

In the above example, void(0) prevents the page from refreshing when the hyperlink is clicked, and instead, a popup window is displayed.

Historical Context of void(0)

Historically, void(0) was used to get the undefined value. In the early days of JavaScript, undefined could be reassigned, leading to potential confusion and bugs in the code.

undefined = "now it's defined"; console.log(undefined); // "now it's defined"

To prevent this and to ensure they were truly getting undefined, developers would use void(0) instead. However, in ECMAScript 5, the ability to reassign undefined was removed, making this use of void(0) largely obsolete.

Alternatives to void(0)

In modern JavaScript development, using void(0) to prevent default actions is seen as outdated. There are better, more readable ways to achieve the same results. One such method is using event.preventDefault().

document.querySelector('a').addEventListener('click', function(event) { event.preventDefault(); // your code here });

This approach is more explicit and self-explanatory, improving code readability and maintainability.


Q: Is void(0) necessary in modern JavaScript?

A: Not really. While void(0) is still valid JavaScript, its primary uses are largely handled by other, more modern techniques. It's more of a relic from JavaScript's past, but understanding it can still provide valuable insights into how the language has evolved.

Q: Can I use other numbers or expressions in place of 0 in void(0)?

A: Yes, you can use any valid JavaScript expression in place of 0. The void operator will evaluate the expression and return undefined, regardless of the expression's value.

Q: Can I use void(0) in all JavaScript environments?

A: Yes, void(0) is valid in all environments where JavaScript can run. That includes browsers, Node.js, and JavaScript-based mobile platforms.

We hope this blog post has shed some light on the purpose and use of void(0) in JavaScript. It's just one of the many nuances that make JavaScript a fascinating language to learn and master. Stay tuned to codedamn for more deep dives into JavaScript's features and quirks!

For a more detailed look at the void operator, check out the official MDN documentation.

Happy coding!

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