`npm start -p 3009` passes your script only `3009` — put script flags after `--`
npm parses dash-prefixed options after the script name itself, even unknown ones, so the flag never reaches your script. `npm start -- -p 3009` passes it through.
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Symptom
A server started with npm start -p 3009 ignores the port, or treats 3009 as a path. For example, a framework CLI reads it as a project directory.
What happens (reproduced)
With "start": "node argv.js", and argv.js printing its arguments:
| Command | The script receives |
|---|---|
npm start -p 3009 |
["3009"] |
npm run start -p 3009 |
["3009"] |
npm start -x 3009 |
["3009"] (even an unknown flag is taken by npm) |
npm start -- -p 3009 |
["-p","3009"] |
Fix
Always separate script arguments with --: npm run <script> -- --flag value.
This matters when a process manager is told to run npm with arguments meant for the underlying tool. Pass them after --, or run the tool's binary directly.
Conditions
- npm
- 11.17.0
- node
- 24.19.0
- observed
- 2026-09-30
Sources
- npm run — Says to use -- to pass dash-prefixed flags and options that would otherwise be parsed by npm.