chai-as-promised@7 with Karma: reserved word 'let'

[haraldrudell]

I am not sure if there is a transpile required or a refrain from fancy new constructs.

Here is the error message:
PhantomJS 2.1.1 (Mac OS X 0.0.0) ERROR
SyntaxError: Use of reserved word 'let' in strict mode
at node_modules/chai-as-promised/lib/chai-as-promised.js:3

affected version: chai-as-promised@7.0.0

Get-around:
npm install chai@3 chai-as-promised@5
-> 3.5.0 + 5.3.0

[domenic]

See https://github.com/domenic/chai-as-promised#browsernode-compatibility

[haraldrudell]

So chai cannot be upgraded until Karma uses the not-yet-released Phantom 2.5?
ariya/phantomjs#14458

[domenic]

Did you read the section I linked?

If your browser doesn't support modern JavaScript syntax, you'll need to transpile it down using a tool like Babel.

[haraldrudell]

So, the solution is to add to the karma config object, a rule inside the webpack field module.rules making the babel-loader process with the test:
test: require.resolve('chai-as-promised'),

and a preprocessors field entry for the same thing:
preprocessors: {
[require.resolve('chai-as-promised')]: ['webpack'],

[baywet]

In my case I don't have control over the webpack config or most of the pipeline. I ended up reverting to 6.0.0 until phantomjs fully supports es6/2015
ariya/phantomjs#14506

[aldencolerain]

If you want more detail on how to do this with Karma Webpack and PhantomJS 5 checkout my comment on the Vue.js issue: vuejs-templates/webpack#646 (comment)
Thanks @haraldrudell for the solution.

[mancioshell]

@haraldrudell i have added your advised configuration in my karma.conf.js, but it still not work, with the same error
PhantomJS 2.1.1 (Windows 7 0.0.0) ERROR
SyntaxError: Use of reserved word 'let' in strict mode

Could you post your solutions please?

Thanks in advance