How can I effectively handle JavaScript errors globally using the `window.onerror` event?

Effective JavaScript Error Handling with Global Event Mechanism

To handle undefined function errors globally, leveraging JavaScript's global event mechanism effectively captures all uncaught exceptions.

window.onerror Event Handling

Implement an event handler for the window.onerror event as follows:

<code class="javascript">window.onerror = function(msg, url, line, col, error) {
  // Message, URL, line and column details
  // Note that col & error are new to HTML 5 and may vary across browsers.

  // Customize the error display or perform error reporting using AJAX, for instance:
  var xhr = new XMLHttpRequest();
  xhr.open('POST', '/ajax/log_javascript_error');
  xhr.send(JSON.stringify({ msg, url, line, col, error }));
};</code>

When does window.onerror Trigger?

This event fires when:

• Uncaught Exceptions: Throwing messages, calling undefined functions, or crossing origin iframe content window/document errors.
• Compile Errors: Syntax errors, such as unmatched brackets, missing semicolons, or attempting to compile non-script arguments.

Browser Support

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

Additional Resources

• Mozilla Developer Network: [window.onerror](https://developer.mozilla.org/en-US/docs/Web/API/GlobalEventHandlers/onerror)
• MSDN: [Handling and Avoiding Web Page Errors Part 2: Run-Time Errors](https://docs.microsoft.com/en-us/previous-versions/ms536764(v=vs.85))
• [Back to Basics – JavaScript onerror Event](https://www.webdesignerdepot.com/2014/10/back-to-basics-javascript-onerror-event/)
• [DEV.OPERA: Better error handling with window.onerror](https://dev.opera.com/articles/better-error-handling-with-window-onerror/)
• [Window onError Event](https://www.html5rocks.com/en/tutorials/developertools/onerror/)
• [Using the onerror event to suppress JavaScript errors](https://stackoverflow.com/a/11712511)
• [SO: window.onerror not firing in Firefox](https://stackoverflow.com/q/5472601/123152)

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