".mts" and ".cts" default format

Shouldn’t the config have these defaults to follow the TypeScript logic?

{
  ".mts": {
    "format": "esm"
  },
  ".cts": {
    "format":  "cjs"
  }
}

One could also argue that these extensions format shouldn’t even be configurable and force these formats, just as .cjs forces commonjs and .mjs forces ecmascript modules

[lukeed]

I understand you, but I don’t think you’re understanding me.

Forcing a format would break this example. That’s because when the src/math.mjs – or src/math.mts for that matter – is loaded, your suggestion would always make it result in ESM syntax (because, natively, it should/is). However, if that were to happen, then the node -r tsm test/math.ts case would have code that looks like this:

// src/math.mjs (converted, forced/remains as ESM)
export const sum = (a, b) => a + b;

// test/math.ts (converted, forced as CJS because of --require hook)
const assert = require('assert');
const math = require('../src/math.mjs');
// ^^ THIS IS STILL ESM -> throws syntax error

Instead, for tsm transpilation, we need to ignore the file’s required format and transform it to the usage’s desired format. This can only work if the converter itself produces semantically correct format conversion … and esbuild does.

So instead, when you run node -r tsm test/math.ts on the above example, you should get this:

// src/math.mjs (converted, forced because of --require hook)
const sum = (a, b) => a + b;
exports.sum = sum;

// test/math.ts (converted, forced because of --require hook)
const assert = require('assert');
const math = require('../src/math.mjs');
// ^^ THIS IS NOW COMMONJS -> success

The semantics are preserved. And the same guarantee happens when you run tsm directly or use --loader tsm except everything is coerced into ESM syntax instead.

[PabloSzx]

your example doesn’t have anything to do with what I mentioned, what I am suggesting is following the Typescript 4.5 new convention of .mts is always ESM and .cts is always CJS, that’s it, following this convention allows you to specify what is the expected format of the transpilation, since I will know that a typescript file with .cts will have “require” available, while “.mts” will always be esm, that’s it