Node "ExperimentalWarning: --loader is deprecated" in CI - Switch to --import

Newer Node deprecated the --loader flag in favor of --import with module.register. The warning is noisy now and the flag will break on a future Node.

What this error means

A CI step that registers a loader (for TypeScript or ESM transforms) prints ExperimentalWarning: --loader is deprecated, and may fail if warnings are treated as errors.

(node:1234) ExperimentalWarning: --loader is deprecated, use register()
or --import instead
(Use `node --trace-warnings ...` to show where the warning was created)

Common causes

Using the deprecated --loader flag

The command registers a loader with --loader, which newer Node deprecates in favor of module.register.

An outdated tool wrapper still passing --loader

A devDependency wrapper invokes Node with --loader under the hood.

How to fix it

Register the loader via --import

1. Create a small register module that calls module.register with your loader.
2. Pass it to Node with --import instead of --loader.

// register.mjs
import { register } from 'node:module';
register('./my-loader.mjs', import.meta.url);

Upgrade the tool that injects --loader

1. Update the tool to a version that uses --import or register.
2. Re-run so the deprecated flag is gone.

How to prevent it

• Move loader registration to --import with module.register, keep loader-using tools current, and avoid relying on flags Node has marked deprecated.

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