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POHow can I override/extend ReferenceError in Chrome's JavaScript?
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copied!<p>To make debugging easier, I'm capturing all of the console logs in Chrome so that users who submit a feedback entry will also submit all of the logs to our server. When someone encounters a problem in production, I can first and foremost get them back to work so that I can then sit down and more thoroughly go through all of the logs to determine the root cause of whatever issue the user encountered in production.</p> <p>The technique I use to capture the logs involves overriding console.log so that all text entered in the first argument gets stored in an array while simultaneously invoking the legacy function so that I can still see the logs in the console too.</p> <p>The problem is when there's the occasional uncaught exception. These aren't included in the uploaded logs, so it's not always clear what caused the problem. So I tried overriding ReferenceError by writing a JavaScript function that takes a function as an argument, then returns a new function that does stuff with it, like storing data in a variable, and then invoking the legacy function as the last step:</p> <pre><code>function overrideException(legacyFn) { /** arguments for original fn **/ return function() { var args = []; args[0] = arguments[0]; // pass in as arguments to original function and store result to // prove we overrode the ReferenceError output = ">> " + legacyFn.apply(this, args).stack; return legacyFn.apply(this, arguments); } } </code></pre> <p>To test the overrideException function, I ran the following code on the console:</p> <pre><code>ReferenceError = overrideException(ReferenceError); </code></pre> <p>Afterwards, I tested the returned function, the new ReferenceError, by manually throwing a ReferenceError:</p> <pre><code>throw new ReferenceError("YES!! IT WORKS! HAHAHA!"); </code></pre> <p>The resulting output on the console is:</p> <blockquote> <p>ReferenceError: YES!! IT WORKS! HAHAHA!</p> </blockquote> <p>And checking the global variable <code>output</code> from the overrideException function shows that it did indeed run:</p> <pre><code>output ">> ReferenceError: YES!! IT WORKS! HAHAHA! at ReferenceError (<anonymous>) at new <anonymous> (<anonymous>:18:35) at <anonymous>:2:7 at Object.InjectedScript._evaluateOn (<anonymous>:562:39) at Object.InjectedScript._evaluateAndWrap (<anonymous>:521:52) at Object.InjectedScript.evaluate (<anonymous>:440:21)" </code></pre> <p>Now, here's where things start to fall apart. In our code, we're not going to know when an uncaught exception occurs, so I tested it by attempting to run a function that doesn't exist:</p> <pre><code>ttt(); </code></pre> <p>Which results in:</p> <blockquote> <p>ReferenceError: ttt is not defined</p> </blockquote> <p>However, unlike the case where we explicitly throw an error, in this case, the function doesn't fire, and we're left with only the legacy functionality. The contents of the variable <code>output</code> is the same as in the first test.</p> <p>So the question seems to be this: <strong>How do we override the ReferenceError functionality that the JavaScript engine uses to throw errors so that it's the same one we use when we throw a ReferenceError?</strong></p> <p>Keep in mind that my problem is limited only to Chrome at this time; I'm building a Chrome Packaged app.</p>

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