k6 cli missing switch to enable Typescript mode

[shoffmeister]

Brief summary

Since the removal of the K6_COMPATIBILITY_MODE=experimental_enhanced environment option, there is no way to run the k6 docker image with Typescript code:

docker run --rm -i grafana/k6 run - <MyTypescriptFile.ts

will always fail.

k6 version

1.0.0

OS

Linux

Docker version and image (if applicable)

k6/1.0.0

Steps to reproduce the problem

The documentation at https://grafana.com/docs/k6/latest/get-started/running-k6/ provides instructions on how to run k6 through docker, i.e.

docker run --rm -i grafana/k6 run - <script.js

Alas, this only works for Javascript and not Typescript, as

docker run --rm -i grafana/k6 run - <MyTypescriptFile.ts

will complain about any type annotation, as k6 has no awareness of the piped stdin is in fact Typescript.

This is very similar to #4199 - except that https://grafana.com/docs/k6/latest/using-k6/javascript-typescript-compatibility-mode/ officially documents that K6_COMPATIBILITY_MODE=experimental_enhanced has been removed. The effect of that, though, is that there is no way to turn on Typescript mode.

Hence: k6 cli missing switch to enable Typescript mode, at least for the official "how to run k6 through docker" documented approach.

Expected behaviour

A cli flag is present that turns on Typescript mode.

After adding that flag, say --typescript, the following command will work,

echo "function log(message: string) {} export default function() {}" | docker run --rm -i grafana/k6:1.0.0 run --typescript -

Actual behaviour

Run

echo "function log(message: string) {} export default function() {}" | docker run --rm -i grafana/k6:1.0.0 run -

and get

time="2025-05-08T06:01:16Z" level=error msg="GoError: file:///-: Line 1:21 Unexpected token :\n" hint="script exception"

[joanlopez]

Hey @shoffmeister,

We recently merged a fix in #5246, that will be part of the upcoming k6 v1.4.0 release.
It makes no mode to be explicitly enabled, but it just tries to strip types (and infer TS) from stdin automatically.

Please, let us as know if there's anything else you're missing. In such case, please open a new issue.
Thanks!