Import statements are hoisted when target is CommonJs

[petkaantonov]

Describe the bug

Import statements are hoisted when target is CommonJS:

import A from "a;
console.log(1);
import B from "a";

Becomes

require(...);
require(...);
console.log(1);

This is incorrect, require calls are normal functions and should have preserved order. Imports should only be hoisted when they are actual es6 imports. This is incompatible with tsc and probably others, tsc keeps the order as expected when output module is commonjs.

Additional context

It was fixed but then reverted in #1457

[mischnic]

With native esm (in Node or in browsers), the following prints "a, b, index"

// index.js
import "./a.js";
console.log("index");
import "./b.js";

// a.js
console.log("a");

// b.js
console.log("b");

And I'd argue that transpiling the code to CJS shouldn't change the behaviour of the code

[petkaantonov]

• It is incompatible with tsc
• It sucks for commonjs users, remember we are forced to use import not because it is better syntax but because typescript types dont work with require
• Most code was written with require in mind, so require order matters
• If you are able to use esm, why compile code to cjs? and why expect the behavior be the same? They are incompatible module systems.

[mischnic]

From my perspective, the real problem is that tsc and Babel/the spec don't agree

I guess swc has to choose a side here.

[kdy1]

This feature is useful for using some of node.js modules, which expect execution order of common js modules.
So I think this behavior should be allowed, but only with a bad-named flag, just like dangerouslySetInnerHTML.
I'll think more about the name of the flag.

[petkaantonov]

Some suggestions: disableImportHoisting, noImportHoist

[devongovett]

Isn't this exactly what the jest mock transform allows already? Do you have a different use case for this? IMO deviating from the spec behavior is a bad idea. TSC is simply wrong.

If you want to imports to behave like require, why not just write require?

[kdy1]

I missed that users can use require.
Thanks, @devongovett !

I think users should use require if the execution order of require is required.

[devongovett]

Also fwiw TSC is planning on changing this. microsoft/TypeScript#39764

[petkaantonov]

Isn't this exactly what the jest mock transform allows already? Do you have a different use case for this? IMO deviating from the spec behavior is a bad idea. TSC is simply wrong.

If you want to imports to behave like require, why not just write require?

TypeScript types don't work with require. When I am compiling TypeScript to CommonJS, the ESM spec has nothing to do with it and its spec should be irrelevant and the commonjs spec should be relevant - which specifies no hoisting. At least a flag should be introduced so that commonjs spec is followed when compiling for commonjs.