Attempted import error with "npm run build", works with "npm start"-CodePudding

I have a React app that runs fine with npm start, but fails to build with the following error when running npm run build:

`Creating an optimized production build...
Failed to compile.

Attempted import error: './parseq-lang.js' does not contain a default export (imported as 'grammar').

The import statement looks like this (you can see the full file here):

import grammar from './parseq-lang.js';

The module being imported is generated code from nearleyc. Its export portion looks like this (you can see the full file here – again this is generated code, so I'd rather not change this if I can avoid it):

(function () {

[...]

if (typeof module !== 'undefined'&& typeof module.exports !== 'undefined') {
   module.exports = grammar;
} else {
   window.grammar = grammar;
}
})();

Does anyone know what might be happening or have any pointers to help me debug? Thanks!

CodePudding user response：

For now I have decided to modify the export in the generated code. Seems like the real fix here is to update nearleyc to generate ES6 compliant code.

CodePudding user response：

It seems nearlyc can generate an ES6 module, see the source code here: https://github.com/kach/nearley/blob/6e24450f2b19b5b71557adf72ccd580f4e452b09/lib/generate.js#L143

Accoring to the section "Using Preprocessors" in https://nearley.js.org/docs/parser you need to put a line @preprocessor module or @preprocessor esmodule at the top of your grammar file.