title: Trace the execution of ALL Javascript in a web app
body: <p>Here is the situation: A complex web app is not working, and it is possible to produce undesired behavior consistently. The cause of the problem is not known.</p>
  
  <p>Proposal: Trace the execution paths of all javascript code. Essentially, produce two monstrous logs which can then be fed into a diff algorithm to determine where the behavior related to the bug begins to diverge (as the cause is not apparent from application behavior, and both comprehending and obtaining a copy of the actual JS code being run is difficult, due to the many pages that must be switched to and copied out from the web inspector. Making it difficult is the fact that all pages are dynamically spliced together with Perl code, where significant portions of JS code exist only as (dynamic...) Perl strings).</p>
  
  <p>The Web Inspector in Chrome does not have an option that I know about for logging an execution trace. Basically what I would like is a log of every line of JS that is executed, in the order that they are executed. I don't see this as being a difficult thing to obtain given that the JS VM is single-threaded. The problem is simply that the existing user-facing tools are not designed for quite this much hardcore debugging. If we look at the Profiler in the Dev Tools, it's clearly capable of the kind of instrumentation that I need, but it is fundamentally designed to do <strong>profiling</strong> instead of <strong>tracing</strong>. </p>
  
  <p>How can I get started with this? Is there some way I can build Chrome from source, where I can </p>
  
  <ul>
  <li>switch off JIT in V8?</li>
  <li>log every single javascript expression evaluated by V8 to a file</li>
  </ul>
  
  <p>I have zero experience with the development side of Chrome. So e.g. links to dev-builds/branches/versions/distros of Chrome/Chromium/Canary (what's the difference?) are welcome.</p>
  
  <p>At this point it appears that instrumenting the browser with powerful js tracing is still likely to be easier than redesigning the buggy app. The architecture of the page is a disaster, but the functionality is complex, and it almost fully works. I just have to find the one missing piece.</p>
  
  <p>Alternatively, if tools of this sort already exist, what are some other keywords I can search for them with? "Code Tracing" is pretty much the only thing I can come up with. </p>
  
  <p>I tested <a href="http://ejohn.org/blog/deep-tracing-of-internet-explorer/" rel="noreferrer">dynaTrace</a>, which was a happy coincidence as our app supports IE (indeed Chrome support just came out of beta), but this does not produce a text dump, it basically produces a <em>massive</em> Win32 UI expando-tree, which is impossible to diff. This makes me really sad because I <em>know</em> how much more difficult it was to make the representation of the trace show up that way, and yet it turns out being almost utterly useless. Who's going to scroll up and down that tree view and see anything really useful in it, in anything other than a toy example of a web app?</p>