preprocessors.shift(...) is not a function

[kentcdodds]

I think this commit is giving me this error:

27 07 2015 15:21:53.351:ERROR [karma]: [TypeError: preprocessors.shift(...) is not a function]
TypeError: preprocessors.shift(...) is not a function
at nextPreprocessor (/Users/kentcdodds/Developer/alianza/admin-portal/node_modules/karma/lib/preprocessor.js:73:28)
at /Users/kentcdodds/Developer/alianza/admin-portal/node_modules/karma/lib/preprocessor.js:96:7
at /Users/kentcdodds/Developer/alianza/admin-portal/node_modules/karma/node_modules/graceful-fs/graceful-fs.js:76:16
at FSReqWrap.readFileAfterClose as oncomplete

Anything off the top of your head? Everything's working fine with version 0.13.1 but breaks with version 0.13.2. Do you know what might be the problem? Or do you need me to dig more?

[dignifiedquire]

Thanks for reporting, you are probably right with the commit, but I have no idea how this could happen, as even [].shift() should not throw this error. So if you could find some details, on how this occurs I would be very grateful.

[kentcdodds]

This is the code that I'm looking at that's blowing up:

preprocessors.shift()(content, file, nextPreprocessor)

I believe that what's being shifted isn't a function. That's what the error means... Digging...

[kentcdodds]

It looks like the line:

instances[name] = injector.get('preprocessor:' + name)

is actually assigning instances[name] to undefined which ultimately gets pushed into the preprocessors (as undefined) and then this error gets thrown.

The preprocessor I'm working with is webpack (I'm using version 1.6.0).

[dignifiedquire]

Right, I see, thanks a lot for digging. So the best thing is probably to a) not do the assignment when it fails and b) ensure when pushing into preprocessors that the element is not undefined.

[kentcdodds]

I agree. In addition, I don't think that this fix will resolve my ultimate issue. Do you know why the webpack preprocessor isn't getting added? Will things work when webpack hasn't yet been added?

[dignifiedquire]

karma-webpack won't work unless you use my fork codymikol/karma-webpack#63 that is probably what you are running into

[kentcdodds]

Ah, I see. Sounds good. I'll subscribe to that PR so I know when it's merged. Thanks for your work on karma! It's beyond invaluable. And thanks for the quick response.

[LPGhatguy]

I just hit this issue today with Karma 0.13.10 on OS X, upgrading from an older version and tyring to get karma-sourcemap-loader to work. Has there been any progress on fixing this?

[yaring]

Same error here with 0.13.11 :/

[gejgalis]

The same error with 0.13.11 on Linux. It works for me on Windows :(
I'm using preprocessor webpack
Node: 0.12.7
NPM: 2.11.3

[vasyl-zubach]

npm install karma@canary fixed the problem for me

[gep13]

Also seeing this issue. Any suggestions on how to fix/work around?

[albohlabs]

@gep13 I've also run in this error when i was using karma-sourcemap-loader cause i forgot to add it to the plugins property.

plugins: [
  …
  'karma-sourcemap-loader'
],

So recheck your karma.conf.js.

[cades]

+1 for karma-live-preprocessor

Edit: I found it's because I forget to put "karma-live-preprocessor" in plugin array. After I add it everything is OK.

[kostia]

Same issue with 0.13.16. 😿

[dignifiedquire]

Please everyone can you test if #1777 works for you? I'm not able to reproduce the issue myself, so I can only guess atm.