How to Detect Unregistered Custom Browser Protocols and Respond Gracefully?

How to Detect Browser's Protocol Handlers and Gracefully Handle Unregistered Custom Protocols

When creating a custom URL protocol handler, it's crucial to anticipate scenarios where the handler is not yet installed in a user's browser. To handle this gracefully, detecting the registered protocol handlers is essential.

Detecting Protocol Handlers

Unfortunately, there is no direct JavaScript method to poll for registered protocol handlers. However, a workaround involves using a combination of timers and event handlers.

Workaround

1. Create a link with the custom protocol and an onclick handler that sets a timer and adds an onblur handler to the window.
2. If the browser handles the link (application X) will load, stealing focus from the window.
3. If the onblur event fires, clear the timer to prevent the workaround from interfering with the newly installed protocol.
4. Otherwise, in 3-5 seconds, let the timer fire and notify the user that the custom application is not installed.

Considerations

This workaround is not bulletproof, but it provides a potential solution. It is best suited for applications that are infrequently accessed. For more critical applications, consider exploring alternative methods such as:

• Server-Side Redirection: Redirect users from the custom protocol link to a webpage that checks for the handler and installs it if necessary.
• Browser Extension: Create a browser extension that provides the custom protocol handler functionality.
• System Integration: Register the protocol handler through system-level libraries to ensure system-wide recognition.

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