HTML offline DOM Event: Reference and Examples

When someone interacts with a webpage, the browser sends events to the relevant JavaScript code. The offline event happens when the browser reports loss of network connectivity.

When offline happens

The browser reports loss of network connectivity.

You can listen for it using addEventListener(). That keeps event handling separate from HTML attributes such as onclick and works well with modern code organization.

A small working example

<p>Try the relevant browser action described below.</p>
<p id="event-status" role="status">Waiting for offline...</p>
<script>
    const eventTarget = window;
    const eventStatus = document.getElementById("event-status");

    if (eventTarget) {
        eventTarget.addEventListener("offline", (eventDetails) => {
            eventStatus.textContent = "offline event received";
            console.log(eventDetails.type, eventDetails.target);
        });
    }
</script>

Reading the code

The browser listens for offline on the relevant target. When the event occurs, the callback receives eventDetails, updates the status message and logs the event name and target in Developer Tools.

Toggle the browser's offline mode; navigator.onLine is only a connectivity hint.

Some events need a specific browser condition, another tab or window, or a Web Component to reproduce. Read the trigger steps carefully before deciding that an event handler is not working.

Try it in your browser

Open the page, show the Console panel, and follow this test: Toggle the browser's offline mode; navigator.onLine is only a connectivity hint. Then change one thing in the example and observe whether the event still fires.

Common Beginner Mistakes

• Expecting offline to fire without its required user action or browser condition.
• Toggle the browser's offline mode; navigator.onLine is only a connectivity hint.
• Adding repeated event listeners without considering cleanup or unwanted side effects.

Key Takeaways

• offline reports the browser reports loss of network connectivity.
• addEventListener("offline", ...) listens for the event on the appropriate target.
• Toggle the browser's offline mode; navigator.onLine is only a connectivity hint.