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
    CSS Animations Between Media Queries

    CSS animations are right up there with sliced bread. CSS animations are efficient because they can be hardware accelerated, they require no JavaScript overhead, and they are composed of very little CSS code. Quite often we add CSS transforms to elements via CSS during...

  • By
    Camera and Video Control with HTML5

    Client-side APIs on mobile and desktop devices are quickly providing the same APIs.  Of course our mobile devices got access to some of these APIs first, but those APIs are slowly making their way to the desktop.  One of those APIs is the getUserMedia API...

Incredible Demos

  • By
    CSS Fixed Positioning

    When you want to keep an element in the same spot in the viewport no matter where on the page the user is, CSS's fixed-positioning functionality is what you need. The CSS Above we set our element 2% from both the top and right hand side of the...

  • By
    Do / Undo Functionality with MooTools

    We all know that do/undo functionality is a God send for word processing apps. I've used those terms so often that I think of JavaScript actions in terms of "do" an "undo." I've put together a proof of concept Do/Undo class with MooTools. The MooTools...

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!