purescript-affjax: Dynamic require

[garyb]

There will be several cases of this, as a pattern like this: https://github.com/slamdata/purescript-affjax/blob/071ca67b3535bd20e33b0765251c35a67278d77f/src/Network/HTTP/Affjax.js#L12 is used in a few libraries - whenever a module supports both node and browser and has a shim for one or the other, pretty much.

[Pauan]

The warning just means that it's using CommonJS in a dynamic way, which isn't allowed with ES6 modules.

In the specific case of purescript-affjax, it seems harmless. It's just doing a dynamic check for whether it's on Node.js or not, so that way it can load polyfills.

The problems happen when the code has imports/exports which aren't at the top level. As long as all the imports/exports are at the top level, then it's probably fine, and you can ignore the warnings.

[garyb]

We could probably use a comment or something for suppressing these warnings, as I know of at least 3 libraries that use this technique (affjax, debug, websockets-simple).

[Pauan]

I don't think the parser keeps the comments in the AST, though, so I don't think that would be a good solution. Perhaps something similar to "use strict";? Something like "ignore warnings";

[garyb]

Hmm, that's unfortunate - I wouldn't want to supress all warnings as it could hide other real issues.

[garyb]

"ignore dynamic require"; maybe? 😉

[Pauan]

I think a comment would work if I used a regexp to parse the comments.

I think the form would be something like // rollup-plugin-purs ignore dynamic require, and similar for module and exports

[Pauan]

Okay, version 1.0.6 added in three comment pragmas:

// rollup-plugin-purs ignore dynamic exports
// rollup-plugin-purs ignore dynamic require
// rollup-plugin-purs ignore dynamic module

The comments must have that exact form, and they must appear at the top-level, without any spaces between the start of the line and the // part of the comment.

Each comment will disable a specific warning.