@johnnyreilly This is the PR, as discussed. I wasn't able to run the tests locally, because of Corporate proxy settings, and some tests are failing. Additionally, I didn't add any tests for this change.

Thanks! I think the test failure is just a flaky test (they're full integration tests and so we get the odd false negative) Just kicked off a test run again.

Great! Thanks for this - the fix will go out with the next release 👍

I'm noticing that this is reporting errors from JS files inside node_modules. Is that expected? I.e. I get a lot more errors running via ts-loader than I do when running via tsc.

Are you running with 2.2.2? Should be resolved now

I'm using version 2.4.1. Example of errors:

ERROR in ./~/react-dom/lib/ReactDOM.js
(43,3): error TS2304: Cannot find name '__REACT_DEVTOOLS_GLOBAL_HOOK__'.

ERROR in ./~/react-dom/lib/ReactDOM.js
(68,16): error TS2304: Cannot find name '__REACT_DEVTOOLS_GLOBAL_HOOK__'.

ERROR in ./~/react-dom/lib/ReactDOM.js
(82,40): error TS2551: Property 'documentMode' does not exist on type 'Document'. Did you mean 'DOCUMENT_NODE'?

Ah sorry, yes, ts-loader 2.2.2, tsc 2.4.1

Also are you excluding node_modules in your webpack.config.js?

@johnnyreilly Yes, I believe so:

{
  module: {
    rules: [
      {
        test: /\.ts$/,
        exclude: /node_modules/,
        use: [
          {
            loader: 'babel-loader',
          },
          {
            loader: 'ts-loader',
            options: {
              entryFileIsJs: true,
            }
          },
        ],
      },
    ]
  }
}

Hmmmm may be an issue then. If you lose the entryFileIsJs option does the problem resolve? (You will need to change the entry file too)

You can try the --skipLibCheck option but I haven't checked that this changes anything.

On the other hand, I am using 2.2.2 with a big mixed project, including lots of JS in node_modules and I haven't seen this issue yet, so this is probably a configuration issue. What does your tsconfig.json look like?

Have you enabled checkJs on that project?

@schmuli @johnnyreilly I spent awhile narrowing this issue down, smallest reproduction case here #577

Thanks for the repro - we appreciate it! I wonder, could you test with ts-loader v2.2.0 please? This was the version prior to @schmuli's change. Does the issue arise with that version?