How to Check if a Browser Has Internet Connection

Checking if a browser has internet connection is a common task, especially in web development. Whether you are developing a web application or just want to ensure your browsing environment is accessible, understanding how to check for an internet connection is crucial. This guide will cover different methods to determine if your browser is online or offline, including practical examples and the latest practices in the industry.

Checking Internet Connection Programmatically

To check the internet connection programmatically, you can use JavaScript to monitor the online/offline status of the browser. Here's a simple example using event listeners:

function onlineFunction() {
    console.log(You are now online!);
}
function offlineFunction() {
    console.log(You are now offline!);
}
(online, onlineFunction);
(offline, offlineFunction);

Before implementing this approach, it would be beneficial to read more about it, including alternative methods and their benefits and drawbacks, as explained in the article How to Detect Browser Is Online or Offline.

Practical Methods to Check Internet Connection

One of the most straightforward ways to check if your browser has internet is to try opening a webpage. For example:

It's important to note that browsers do not inherently know about the internet connection; they simply make requests and responses based on user actions. When you click on a link, the browser tries to fetch the data. If you are connected to the internet, the data fetch will be successful with a status of 200. If you are not connected, you will receive an error, such as:

There is no Internet connection
Troubleshoot by checking the network cables, modem, and router. Try reconnecting to Wi-Fi.

However, unless you actively click or access a resource, the browser does not check your internet connection. Many websites today are constantly checking for this and notifying the user. Nevertheless, checking the internet connectivity is a feature optional to the browser, not a functionality it provides by default.

How Browsers Determine Internet Connection

Your computer typically determines internet connection by trying to resolve a DNS name. The browser starts by attempting to request a web resource, usually not HTTPS, to avoid redirection issues with secure websites. In Firefox's case, a lookup is made to a web resource that does not involve HTTPS. If this attempt is unsuccessful, you are notified that your browser is not connected to the internet.

This process can vary based on your browser and operating system. Firefox, for example, will display a message if it cannot resolve the DNS query, showing it as offline. Chrome, on the other hand, will display this in the fine print.

Another potential issue could be a DNS lookup showing an NXDOMAIN failure, which Firefox will indicate as offline, whereas Chrome might display it in the detailed error message.