Don't run karma.conf.js through TS when "allowJs": true

[webmaster128]

I have a project with "allowJs": true in tsconfig.json where I get errors like this:

31 05 2020 15:49:10.978:ERROR [config]: Error in config file!
  TypeError: karma.conf.js: Emit skipped
    at getOutput (/project/node_modules/ts-node/src/index.ts:560:17)
    at Object.compile (/project/node_modules/ts-node/src/index.ts:762:32)
    at Module.m._compile (/project/node_modules/ts-node/src/index.ts:841:43)
    at Module._extensions..js (internal/modules/cjs/loader.js:991:10)
    at Object.require.extensions.<computed> [as .js] (/project/node_modules/ts-node/src/index.ts:844:12)
    at Module.load (internal/modules/cjs/loader.js:811:32)
    at Function.Module._load (internal/modules/cjs/loader.js:723:14)
    at Module.require (internal/modules/cjs/loader.js:848:19)
    at require (internal/modules/cjs/helpers.js:74:18)
    at Object.parseConfig (/project/node_modules/karma/lib/config.js:358:22)

This unexpected behaviour here is that karma.conf.js is interpreted by ts-node. The explanation for this behaviour is here:

TypeScript Node works by registering the TypeScript compiler for .tsx? and .jsx? (when allowJs == true) extensions.

from https://github.com/TypeStrong/ts-node#how-it-works, which is used by require('ts-node').register() in Karma's lib/config.js.

I think only .ts config files should be handled by ts-node.

[devoto13]

This looks like a duplicate of #3329.

[devoto13]

I'll close this in favour of #3329 which has more discussions.