Error when loading modules without export using AMD and outFile options

[micnic]

TypeScript Version: 2.5.2

Code

// a.ts
console.log('A');

// main.ts
import './a';

// main.js (output file of the command "tsc -m amd --outFile main.js main.ts")
console.log('A');
define("main", ["require", "exports", "./a"], function (require, exports) {
    "use strict";
    Object.defineProperty(exports, "__esModule", { value: true });
});

// When running the following error appear:
// Uncaught Error: Script error for "a", needed by: main

gist attached: https://gist.github.com/micnic/eea64a938858e9450bc6a2992cb0105c

Expected behavior:
It is expected that the content of the files which are imported without export statement is concatenated without being wrapped in a closure and they are not required anymore in the output file.

Actual behavior:
When running the code I get the error that the file ./a can not be found. This happens because these files are still required in the context of main.ts closure in the output file.

[kitsonk]

Duplicate of #18232

[micnic]

@kitsonk it is not really the same, the problem is that the a.ts is concatenated and after, when it is no more "visible", it is required like a normal module

[kitsonk]

It is the same, you are trying to load it as a module, but it is being emitted as global JavaScript, and thereby cannot be loaded as a module. Just because you are concatenating to a single file is immaterial.

[micnic]

Sorry, but you did not get my point, I created a gist for this use case: https://gist.github.com/micnic/eea64a938858e9450bc6a2992cb0105c

please download it as zip, unpack it, run tsc in the terminal in the directory, open the browser and check the browser console

[kitsonk]

I did get your point.

a.ts is being emitted as global/plain JavaScript, instead of a module that can be loaded. This is because TypeScript considers any TypeScript file without imports or exports as a global JavaScript file, not a module that can be loaded.

The outFile and the AMD target are red herrings to the root problem. Your problem would go away if you added:

console.log('A');

export let undefined;

to a.ts. Try it, you will notice it fixes your problem. But it is a workaround versus a solution.

[aluanhaddad]

@kitsonk The linked code works fine when tsc emits individual files but fails when outFile is used. This behavior differs from tools such as r.js which emits a named define for a'.

[kitsonk]

@aluanhaddad depends on what the behaviour is though. Obviously console.log('A'); is a non-sensical construct. The transpiler is not emitting it as a module and that could cause problems depending on the use case. But yes, I can see how the behaviour changes between the outFile or not, but the root cause is still that it isn't being emitted as a module, which only exhibits itself when the files are concatenated.

[mhegazy]

The ts compiler defines a module as a file with at least one top-level import/export statement. a file with neither is considered a global script. these assumptions are needed to allow for correct parsing of the files, since modules are parsed in strict mode.
This is a problem with the module spec on TC39's side, that favored web loading over other tools like node, which makes loading modules non-statically determined. there is a proposal to add a paragma "use module"; to eliminate this ambiguity.
since modules with no imports or exports are rare, we recommend using export {}; to your file to force treating it as a module.

[micnic]

ok, thanks for the explanation, I think this issue can be closed