Strange behavior with import statement

[pomeh]

Hello,

In the lib documentation, you instruct to import the jslib url to use the new URL syntax, and it works as expected:

$ cat url.js && \
  echo "----------" && \
  docker run --rm -v $(pwd)/:/usr/local/me docker.io/grafana/k6:0.42.0 run /usr/local/me/url.js

import { URL } from "https://jslib.k6.io/url/1.0.0/index.js";

export default function main() {
    console.log('main');

    console.log('url', new URL('http://example.com'));

    console.log('end');
}
----------

          /\      |‾‾| /‾‾/   /‾‾/   
     /\  /  \     |  |/  /   /  /    
    /  \/    \    |     (   /   ‾‾\  
   /          \   |  |\  \ |  (‾)  | 
  / __________ \  |__| \__\ \_____/ .io

  execution: local
     script: /usr/local/me/url.js
     output: -

  scenarios: (100.00%) 1 scenario, 1 max VUs, 10m30s max duration (incl. graceful stop):
           * default: 1 iterations for each of 1 VUs (maxDuration: 10m0s, gracefulStop: 30s)

time="2023-01-19T10:36:21Z" level=info msg=main source=console
time="2023-01-19T10:36:21Z" level=info msg="url \"http://example.com/\"" source=console
time="2023-01-19T10:36:21Z" level=info msg=end source=console

running (00m00.0s), 0/1 VUs, 1 complete and 0 interrupted iterations
default ✓ [ 100% ] 1 VUs  00m00.0s/10m0s  1/1 iters, 1 per VU

     data_received........: 0 B 0 B/s
     data_sent............: 0 B 0 B/s
     iteration_duration...: avg=410.55µs min=410.55µs med=410.55µs max=410.55µs p(90)=410.55µs p(95)=410.55µs
     iterations...........: 1   1953.872967/s

The log line msg="url \"http://example.com/\" proves it worked.

---

When I comment the import statement, I get an expected error ReferenceError: URL is not defined, that's okay:

$ cat url.js && \
  echo "----------" && \
  docker run --rm -v $(pwd)/:/usr/local/me docker.io/grafana/k6:0.42.0 run /usr/local/me/url.js

// import { URL } from "https://jslib.k6.io/url/1.0.0/index.js";

export default function main() {
    console.log('main');

    console.log('url', new URL('http://example.com'));

    console.log('end');
}
----------

          /\      |‾‾| /‾‾/   /‾‾/   
     /\  /  \     |  |/  /   /  /    
    /  \/    \    |     (   /   ‾‾\  
   /          \   |  |\  \ |  (‾)  | 
  / __________ \  |__| \__\ \_____/ .io

  execution: local
     script: /usr/local/me/url.js
     output: -

  scenarios: (100.00%) 1 scenario, 1 max VUs, 10m30s max duration (incl. graceful stop):
           * default: 1 iterations for each of 1 VUs (maxDuration: 10m0s, gracefulStop: 30s)

time="2023-01-19T10:36:30Z" level=info msg=main source=console
time="2023-01-19T10:36:30Z" level=error msg="ReferenceError: URL is not defined\n\tat main (file:///usr/local/me/url.js:6:27(9))\n\tat native\n" executor=per-vu-iterations scenario=default source=stacktrace

running (00m00.0s), 0/1 VUs, 1 complete and 0 interrupted iterations
default ✓ [ 100% ] 1 VUs  00m00.0s/10m0s  1/1 iters, 1 per VU

     data_received........: 0 B 0 B/s
     data_sent............: 0 B 0 B/s
     iteration_duration...: avg=163.35µs min=163.35µs med=163.35µs max=163.35µs p(90)=163.35µs p(95)=163.35µs
     iterations...........: 1   2399.612223/s

---

Things are getting strange when I import the lib but with a different syntax (import whatever from "https://jslib.k6.io/url/1.0.0/index.js";):

$ cat url.js && \
  echo "----------" && \
  docker run --rm -v $(pwd)/:/usr/local/me docker.io/grafana/k6:0.42.0 run /usr/local/me/url.js

import whatever from "https://jslib.k6.io/url/1.0.0/index.js";

export default function main() {
    console.log('main');

    console.log('uu', new URL('http://example.com'));

    console.log('end');
}
----------
time="2023-01-19T10:48:01Z" level=info msg=main source=console
time="2023-01-19T10:48:01Z" level=info msg="uu \"http://example.com/\"" source=console
time="2023-01-19T10:48:01Z" level=info msg=end source=console

          /\      |‾‾| /‾‾/   /‾‾/   
     /\  /  \     |  |/  /   /  /    
    /  \/    \    |     (   /   ‾‾\  
   /          \   |  |\  \ |  (‾)  | 
  / __________ \  |__| \__\ \_____/ .io

  execution: local
     script: /usr/local/me/url.js
     output: -

  scenarios: (100.00%) 1 scenario, 1 max VUs, 10m30s max duration (incl. graceful stop):
           * default: 1 iterations for each of 1 VUs (maxDuration: 10m0s, gracefulStop: 30s)

time="2023-01-19T10:48:01Z" level=info msg=main source=console
time="2023-01-19T10:48:01Z" level=info msg="uu \"http://example.com/\"" source=console
time="2023-01-19T10:48:01Z" level=info msg=end source=console

running (00m00.0s), 0/1 VUs, 1 complete and 0 interrupted iterations
default ✓ [ 100% ] 1 VUs  00m00.0s/10m0s  1/1 iters, 1 per VU

     data_received........: 0 B 0 B/s
     data_sent............: 0 B 0 B/s
     iteration_duration...: avg=560.56µs min=560.56µs med=560.56µs max=560.56µs p(90)=560.56µs p(95)=560.56µs
     iterations...........: 1   1447.502696/s

Note: for an unknown reason, this docker command did not show all k6 output, so I had to change it as follows:

docker run --name k6 -v $(pwd)/:/usr/local/me docker.io/grafana/k6:0.42.0 run /usr/local/me/url.js > /dev/null && \
docker logs k6 && \
docker rm k6

The JS statement import whatever from "https://jslib.k6.io/url/1.0.0/index.js"; import the lib, and stores its defaults export into whatever variable, and this variable is not used.

But then, the new URL works ! Like if the URL was added in a global namespace when the https://jslib.k6.io/url/1.0.0/index.js file is executed.

This even works with multiple files: if I have 3 files A, B and C using new URL, if only file A import the jslib url, both B and C files can use the new URL syntax without explicitly importing the lib.