How can I globally catch all JavaScript errors, including undefined function calls triggered by Flash, using the `window.onerror` mechanism?

JavaScript's Global Error Mechanism

Problem: Is there a global way to trap every JavaScript error, including undefined function calls triggered by Flash?

Solution Using window.onerror

JavaScript offers a global event handler, window.onerror, that captures errors thrown either during runtime (uncaught exceptions) or compilation (compile-time errors).

<code class="javascript">window.onerror = function(msg, url, line, col, error) {
  // Process and display error information
}</code>

Setting the window.onerror event handler as shown above will intercept and process every error encountered within the JavaScript code.

Types of Errors Handled by window.onerror

window.onerror handles both uncaught exceptions and compile-time errors. Uncaught exceptions include errors like:

• throw "some messages"
• Calling undefined functions like call_something_undefined()

Compile-time errors, on the other hand, include errors such as:

• Unterminated script tags (<script>{</script>)
• Syntax errors (<script>for(;)</script>)

Browser Compatibility

window.onerror is widely supported in modern browsers, including:

• Chrome 13
• Firefox 6.0
• Internet Explorer 5.5
• Opera 11.60
• Safari 5.1

Advanced Usage

Suppression of Browser Error Alerts: By returning true from window.onerror, you can suppress the default browser alert that would normally appear for JavaScript errors.

AJAX Error Reporting: Using XMLHttpRequest, you can send detailed error information via AJAX to a server-side script for logging or further processing.

References

• Mozilla Developer Network: window.onerror ([link](https://developer.mozilla.org/en-US/docs/Web/API/GlobalEventHandlers/onerror))
• MSDN: Handling and Avoiding Web Page Errors Part 2: Run-Time Errors ([link](https://docs.microsoft.com/en-us/previous-versions/aspnet/bb264952(v=vs.100)))
• Back to Basics – JavaScript onerror Event ([link](https://javascriptweblog.wordpress.com/2010/02/11/back-to-basics-javascript-onerror-event/))
• DEV.OPERA: Better error handling with window.onerror ([link](https://dev.opera.com/articles/window-onerror/))
• Window onError Event ([link](https://www.byterocket.org/blog/window-onerror-event))
• Using the onerror event to suppress JavaScript errors ([link](https://remysharp.com/2010/10/08/using-the-onerror-event-to-suppress-javascript-errors/))
• Stack Overflow: window.onerror not firing in Firefox ([link](https://stackoverflow.com/questions/10714399/window-onerror-not-firing-in-firefox))

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