Do I ever need explicit allowSyntheticDefaultImports if esModuleInterop is true configuring TypeScript transpilation?

Question

I need confirmation on the following theory. According to TS docs, there are two options that can be set in tsconfig.json.

1. --allowSynth

Answer 1

If you mean can you leave allowSyntheticDefaultImports undefined and define only esModuleInterop, the answer should be YES moving forward, but there has been an issue with this. PR #26866 seems to be a fix, only merged September 17, so it there may be some risk in the short term.

As why both exist, I believe these were both a part of addressing compatibility issues with imports of Babel-transpiled modules, the original PR added the allowSyntheticDefaultImports option to certain compile-time messages, but in practice didn't address the runtime behavior of the imports. So --esModuleInterop was added later. See TypeScript-Handbook/#816 for discussion of how to update the docs...