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copied!<h1>How to Catch Unhandled Javascript Errors</h1> <p>Assign the <code>window.onerror</code> event to an event handler like:</p> <pre><code><script type="text/javascript"> window.onerror = function(msg, url, line, col, error) { // Note that col & error are new to the HTML 5 spec and may not be // supported in every browser. It worked for me in Chrome. var extra = !col ? '' : '\ncolumn: ' + col; extra += !error ? '' : '\nerror: ' + error; // You can view the information in an alert to see things working like this: alert("Error: " + msg + "\nurl: " + url + "\nline: " + line + extra); // TODO: Report this error via ajax so you can keep track // of what pages have JS issues var suppressErrorAlert = true; // If you return true, then error alerts (like in older versions of // Internet Explorer) will be suppressed. return suppressErrorAlert; }; </script> </code></pre> <p>As commented in the code, if the return value of <code>window.onerror</code> is <code>true</code> then the browser should suppress showing an alert dialog.</p> <h2>When does the window.onerror Event Fire?</h2> <p>In a nutshell, the event is raised when either 1.) there is an uncaught exception or 2.) a compile time error occurs.</p> <blockquote> <p><strong>uncaught exceptions</strong></p> <ul> <li>throw "some messages"</li> <li>call_something_undefined();</li> <li>cross_origin_iframe.contentWindow.document;, a security exception</li> </ul> <p><strong>compile error</strong></p> <ul> <li><code><script>{</script></code></li> <li><code><script>for(;)</script></code></li> <li><code><script>"oops</script></code></li> <li><code>setTimeout("{", 10);</code>, it will attempt to compile the first argument as a script</li> </ul> </blockquote> <h2>Browsers supporting window.onerror</h2> <ul> <li>Chrome 13+</li> <li>Firefox 6.0+</li> <li>Internet Explorer 5.5+</li> <li>Opera 11.60+</li> <li>Safari 5.1+</li> </ul> <h2>Screenshot:</h2> <p>Example of the onerror code above in action after adding this to a test page:</p> <pre><code><script type="text/javascript"> call_something_undefined(); </script> </code></pre> <p><img src="https://i.stack.imgur.com/cl91I.png" alt="Javascript alert showing error information detailed by the window.onerror event"></p> <h2>JSFiddle:</h2> <p><a href="https://jsfiddle.net/nzfvm44d/" rel="noreferrer">https://jsfiddle.net/nzfvm44d/</a></p> <h2>References:</h2> <ul> <li><a href="https://developer.mozilla.org/en/DOM/window.onerror" rel="noreferrer">Mozilla Developer Network :: window.onerror</a></li> <li><a href="http://msdn.microsoft.com/en-us/library/ms976144.aspx" rel="noreferrer">MSDN :: Handling and Avoiding Web Page Errors Part 2: Run-Time Errors</a></li> <li><a href="http://blogs.microsoft.co.il/blogs/gilf/archive/2011/11/23/back-to-basics-javascript-onerror-event.aspx" rel="noreferrer">Back to Basics – JavaScript onerror Event</a></li> <li><a href="http://dev.opera.com/articles/view/better-error-handling-with-window-onerror/" rel="noreferrer">DEV.OPERA :: Better error handling with window.onerror</a></li> <li><a href="http://www.mattsnider.com/window-onerror-event/" rel="noreferrer">Window onError Event</a></li> <li><a href="http://www.javascriptkit.com/javatutors/error2.shtml" rel="noreferrer">Using the onerror event to suppress JavaScript errors</a></li> <li><a href="https://stackoverflow.com/q/1008692/590956">SO :: window.onerror not firing in Firefox</a></li> </ul>

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