@DanielRosenwasser @RyanCavanaugh @orta Do you think the new behaviour is reasonable?

@sheetalkamat @weswigham Is createProgram the right place to put this?

For other defaulted flags dependent on other flags, we have something like a getStrictCompilerOptionValue helper that we use everywhere rather than checking the compiler options directly (no, I don't think createProgram handles all inputs - transpileModule is notable for probably being unaffected). You should probably add a getAllowJSCompilerOption helper that we use everywhere rather than checking the flags directly.

I thought that might be the case. I switched to an accessor function getAllowJSCompilerOption instead.

I'm not so sure how I feel about this. But I can't think of any reason why it's bad.

Chatted with @RyanCavanaugh, he couldn't either.

He also pointed out that maybe allowJs should default to true now. I'll investigate that next.