windows-npm-run-script-shell

name	windows-npm-run-script-shell
description	Use when Windows npm run, npm test, npm run build, or npm run-script exits before running the script with ERR_INVALID_ARG_TYPE, "file argument must be of type string", missing ComSpec, broken script-shell, stripped CLI flags, sandboxed npm cache/log EPERM, or silent npm script output.

Windows Npm Run Script Shell

Overview

Windows npm scripts need a shell. If ComSpec is missing or npm cannot infer a script shell, npm run ... can fail inside npm before tsc, Vite, Vitest, or Playwright actually runs.

Triage

Use this flow before changing app code:

1. Run the target tool directly with npx, for example npx tsc -b --pretty false, npx vite build, or npx vitest run.
2. Run npm run <script> --loglevel verbose.
3. Open the npm debug log if output is empty.
4. Check shell config:

npm config get script-shell
npm config get cache
npm config get update-notifier
Write-Host "ComSpec=[$env:ComSpec]"
Write-Host "SHELL=[$env:SHELL]"

If direct npx commands pass but npm run fails with ERR_INVALID_ARG_TYPE: The "file" argument must be of type string. Received undefined, treat it as npm shell configuration, not a project build failure.

If direct node <script> succeeds but npm test/npm run exits silently in a sandbox, rerun with --loglevel verbose. When npm reports EPERM creating %LocalAppData%\npm-cache\_logs or attempts registry access only for update checks, treat it as npm runtime side effects, not a test failure.

Fix

Prefer a project-local .npmrc so the fix travels with the repo:

script-shell=C:\Windows\System32\cmd.exe

For sandboxed Windows workspaces where npm cannot write the user cache/log directory, keep npm side effects inside the repo and disable network-prone notices:

cache=.npm-cache
update-notifier=false
fund=false
audit=false
script-shell=cmd.exe

Then rerun:

npm run build
npm test -- --run

If the project requires PowerShell syntax in scripts, set script-shell to PowerShell and avoid && in package scripts, because Windows PowerShell 5 does not support &&.

Common Mistakes

• Do not rewrite TypeScript, Vite, Vitest, or React code when npx <tool> succeeds and only npm run fails.
• Do not treat silent npm output as proof that the build tool produced no diagnostics; inspect the npm debug log.
• Do not ignore npm cache/log EPERM in sandboxed workspaces; set a project-local cache before escalating.
• Do not set a global npm config unless the user asked for machine-wide changes.
• Do not assume SHELL replaces ComSpec for npm on Windows.

Completion Standard

The issue is fixed only when:

• The original npm run <script> command succeeds.
• The direct tool command still succeeds.
• Tests/builds that previously passed via npx also pass through npm scripts.