nyc + mocha + es6 modules

Question

I am trying to use nyc + mocha to get test coverage on my unit tests that uses the es6 module syntax. When I run mocha my_test.mjs everything works fine. The dependencies within my_test.mjs (using native import) are resolved correctly. But when I prepend this command with nyc: nyc mocha my_test.mjs it doesn't work anymore, throwing this error:

node_modules/mocha/lib/esm-utils.js:6
    return import(url.pathToFileURL(file));
           ^^^^^^

SyntaxError: Unexpected token import
    at Module._extensions..js (module.js:663:10)
    at Object.replacementCompile (nodejs/core/tests/cache.install.nodejs_install/node_modules/append-transform/index.js:60:13)
    at Module._extensions..js (module.js:663:10)

I tried different variants nyc --require esm mocha my_test.mjs or forcing --experimental-modules with node but nothing seems to work.

Note, I am using the latest version of node, nyc and mocha

Any idea?

Have you tried updating to Node 14? – GOTO 0 Jun 22 '20 at 09:26 — GOTO 0, Jun 22 '20 at 09:26

score 6 · Answer 1 · edited Dec 12 '20 at 23:08

6

For anybody who finds this by searching, the c8 code coverage tool was a drop in replacement for me. I literally just installed it and replaced 'nyc' with 'c8' in my package.json scripts.

Also, here is the open (at the time I wrote this) nyc issue if you are curious: https://github.com/istanbuljs/nyc/issues/659

edited Dec 12 '20 at 23:08

Dharman

26,923
21
73
125

answered Dec 12 '20 at 23:03

Dave Welling

1,520
1
15
13

1

Thank you Dave that worked for me! The guy behind that project is totally underated! Benjamin, in case you read this one day - you are a lifesaver. – Henry Ruhs Oct 26 '21 at 22:28

Annenarg · Answer 2 · 2020-07-02T12:56:40.923

I encountered the same issue after updating my dependencies. I updated to mocha version 8.x, while still using mocha.opts for configuration.

#4175: Having been deprecated with a warning since v7.0.0, mocha.opts is no longer supported

See the release notes: https://github.com/mochajs/mocha/releases/tag/v8.0.0

Reverting back to mocha 7.x helped me in the end*. If you don't want to use mocha 7 or older, you can replace mocha.opts with a configuration file: https://mochajs.org/#configuring-mocha-nodejs

*note: On the way, I also added

"@types/node": "14.0.14",
"@types/mocha": "7.0.2",

to package.json. My nyc version is "nyc": "15.1.0", But I am not sure if that is necessary to solve your problem.

score 0 · Answer 3 · answered Jul 27 '20 at 12:50

At the risk of seeming patronising; I noticed above you said you were on 14.4.0 do double check your version. I thought I was on 14.x because I had updated my package.json and when I typed:

npm list | grep node

I got:

+-- @types/node@14.0.26
+-- nodemon@2.0.4
+-- ts-node@8.10.2

I'm newby to Node enough to get tripped up. If I typed:

node --version

Then I found I was on a much older one.

Once I updated to the latest version (14.6.0) this error went away. I'm using Windows so had to download the latest from nodejs.org.

score 0 · Answer 4 · answered Sep 18 '20 at 10:20

0

It looks you have an old nodejs version, follow link below to upgrade your node version: Had same issue and am fine now!

How do I update Node.js?

answered Sep 18 '20 at 10:20

Trevor Nathan

361
2
9

score -2 · Answer 5 · edited Jul 12 '20 at 21:58

-2

I have the same problem with you。Actually，I revise this file
node_modules/mocha/lib/esm-utils.js
from

return import(url.pathToFileURL(file));

to

return require(url.pathToFileURL(file));

it can works.

edited Jul 12 '20 at 21:58

vimuth

4,137
13
61
97

answered Jul 12 '20 at 08:46

user13915800

13
2

1

I don't think that changing node_modules/mocha (or any file in node_modules directly) is a good practice. – RtmY Oct 11 '20 at 17:11

nyc + mocha + es6 modules

5 Answers5