Force Stack Traces with JavaScript

By  on  

I recently inherited a Node.js project and man is that scary.  The code was well written but whenever you inherit a project you instantly inherit the fear of messing things up.  My goal was to fix a fairly routine bug, and finding the issue was fairly easy, but tracing through the code to figure out what called what and what passed what was a nightmare.

So I did the only thing I could do to figure out WTF was going on:

// The magic
console.log(new Error().stack);

/* SAMPLE:

Error
    at Object.module.exports.request (/home/vagrant/src/kumascript/lib/kumascript/caching.js:366:17)
    at attempt (/home/vagrant/src/kumascript/lib/kumascript/loaders.js:180:24)
    at ks_utils.Class.get (/home/vagrant/src/kumascript/lib/kumascript/loaders.js:194:9)
    at /home/vagrant/src/kumascript/lib/kumascript/macros.js:282:24
    at /home/vagrant/src/kumascript/node_modules/async/lib/async.js:118:13
    at Array.forEach (native)
    at _each (/home/vagrant/src/kumascript/node_modules/async/lib/async.js:39:24)
    at Object.async.each (/home/vagrant/src/kumascript/node_modules/async/lib/async.js:117:9)
    at ks_utils.Class.reloadTemplates (/home/vagrant/src/kumascript/lib/kumascript/macros.js:281:19)
    at ks_utils.Class.process (/home/vagrant/src/kumascript/lib/kumascript/macros.js:217:15)
*/

Of course the actual "error" doesn't matter -- the stack trace is exactly what you need to figure out what's calling what up the chain. When available you can also use console.trace() (when available) to achieve roughly the same output.  You can thank me later!

Recent Features

  • By
    JavaScript Promise API

    While synchronous code is easier to follow and debug, async is generally better for performance and flexibility. Why "hold up the show" when you can trigger numerous requests at once and then handle them when each is ready?  Promises are becoming a big part of the JavaScript world...

  • By
    Write Simple, Elegant and Maintainable Media Queries with Sass

    I spent a few months experimenting with different approaches for writing simple, elegant and maintainable media queries with Sass. Each solution had something that I really liked, but I couldn't find one that covered everything I needed to do, so I ventured into creating my...

Incredible Demos

Discussion

  1. Roman

    How about console.trace()?

    • console.trace() doesn’t exist on Chrome on Android.

  2. MaxArt

    How about node-inspector? It lets you use Chrome’s developer tools (sort of) to set breakpoints and inspect the code.
    I’m not debugging any node project without it anymore!

  3. Stuart

    Linked from JavaScript Daily. You can also use node debug whatever.js and put a debugger; statement in the location you want to inspect. Then the bt command will give you the trace.

  4. This is the solution I always use on my apps:

    https://gist.github.com/Venerons/f54b7fbc17f9df4302cf

    You can’t have more info than this. Really.

  5. Loupax

    I used to just call an undefined function in order to make an error appear. Lazy means to the same end I’d say

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!