Node: "Just My Code" for stack traces?

[benjamingr]

Throwing a raw idea out there:

I just saw this question where a user was confused about a stack trace they got when using puppeteer:

Unhandled Rejection at: Promise Promise {
  <rejected> Error: Navigation Timeout Exceeded: 30000ms exceeded
    at Promise.then (C:\...\pupet test\node_modules\pupp
eteer\lib\NavigatorWatcher.js:71:21)
    at <anonymous> } reason: Error: Navigation Timeout Exceeded: 30000ms exceede
d
    at Promise.then (C:\...\pupet test\node_modules\pupp
eteer\lib\NavigatorWatcher.js:71:21)
    at <anonymous>

The point is, the first few stack frames are irrelevant to the user. If the first stack frame showed the part in _their_ code that caused the error it would have been a lot more useful.

I'm wondering if we can improve the debugging experience of users by giving them "Just My Code"

Just My Code

Node could expose a "Just My Code" exception mode similar to the way stacks work in the Chrome devtools. Running Node with the flag would hide any frames from node_modules folder.

Thoughts?

[apapirovski]

Seems pretty well suited to the user-land, no? Just use a custom Error.prepareStackTrace that filters out Node.js core modules & node_modules code. There are some edge cases but I don't think that's a good reason to make it be a part of the core.

(Can also do all kinds of other neat things with the API https://github.com/v8/v8/wiki/Stack-Trace-API)

[bnoordhuis]

One argument in favor is that only core can disambiguate stack frames with 100% certainty.

vm.runInThisContext('throw new TypeError()', {filename:'vm.js'}) throws an exception that _looks_ like it comes from the vm module, but doesn't, and there's really no way for a user land hook to tell.

That said, I don't necessarily think hiding stack frames is a good idea. I can quickly see that turning into a bigger hindrance than a help, with people filing bug reports with unhelpful stack traces. Getting a good bug report is already more the exception than the norm, in this day and age.

[techsin]

maybe a plugin that make colors of files in node_modules gray and less contrast so you can see what file are yours

[jasnell]

If it can be done reasonably well I think this would be excellent to have but I definitely share @bnoordhuis' concern around it. It wouldn't hurt to have some non-committal experimentation around it.

[techsin]

so what im saying wont hide it, but only visually color it differently in terminal.

[techsin]

i created a simple script that accomplishes what i was thinking....
I simply put it in main app.js file

const colors = require('colors');
Error.prepareStackTrace = (err, arr) => {
   let lines = err.stack.split('\n');
   lines = lines.map(x => x.includes('node_modules') ? colors.grey(x) : x);
   lines = lines.join('\n');
   err.stack = lines;
};

then in one of my routes of app

throw new Error('test');

result ....

https://github.com/v8/v8/wiki/Stack-Trace-API

[AyushG3112]

Problem with just different Coloring is when you use SDKs which transfer the flow of control a lot.

I use the aws-sdk a lot and the stack traces there are not useful because it is filled with the stack of the internal function calls, hiding frames from node_modules option will help a lot in this case.

[techsin]

didn't explain how coloring won't help sdk traces which live in node_modules...

[joyeecheung]

Just realize that we have a default Error.stackTraceLimit = 10, so unless users set this to a higher value, many of our internal stack frames are probably not going to be visible to them anyway if their code throws in a sufficiently deep call stack.

Another idea would be to exclude all the stack frames up to the first frame of user code (on master it's usually Module._compile and 8 frames below)

[BridgeAR]

This is partially fixed since a while. Using console.log or util.inspect on errors marks Node.js stack frames grey and adds an underscore to node_modules names. We could go ahead and add a color to node_modules frames but not everyone wanted that. Should this stay open or shall we consider it as solved?

[jasnell]

I'd say let's consider it solved. If someone wishes to make further enhancements, a PR with a concrete proposal would be ideal. Closing