How npm run Executes Scripts and Uses node_modules/.bin in Vue CLI Projects

The piece is framed as a mock interview where the candidate is asked what actually happens when the command npm run xxx is executed, leading to a detailed technical explanation.

npm first reads the project's package.json to find a matching entry in the scripts section; for example, npm run serve maps to the command vue-cli-service serve.

The reason the raw binary vue-cli-service cannot be run directly is that it is not a globally installed executable. During npm i, npm creates a symlink (or wrapper) for each package's declared binary inside node_modules/.bin, and automatically adds this directory to the process $PATH.

When npm run serve is invoked, npm resolves the script to vue-cli-service serve and actually runs ./node_modules/.bin/vue-cli-service serve. This works even without a global installation because the local .bin link points to the package's executable script.

If a package is installed globally with npm install -g xxx, its binary is linked to a global node_modules/.bin directory, making the command available system‑wide.

@ECHO off
GOTO start
:find_dp0
SET dp0=%~dp0
EXIT /b
:start
SETLOCAL
CALL :find_dp0

IF EXIST "%dp0%
ode.exe" (
  SET "_prog=%dp0%
ode.exe"
) ELSE (
  SET "_prog=node"
  SET PATHEXT=%PATHEXT:;.JS;=;%
)

endLocal & goto #_undefined_# 2>NUL || title %COMSPEC% & "%_prog%" "%dp0%\..\@vue\cli-service\bin\vue-cli-service.js" %*

On Windows the .cmd wrapper ( vue-cli-service.cmd) ultimately calls node to execute vue-cli-service.js, while on Unix‑like systems the plain vue-cli-service binary is used.

Running npm run xxx makes npm search node_modules/.bin for the executable and runs it if found.

If not found locally, npm falls back to the global node_modules/.bin (installed with -g).

When neither location contains the binary, the system PATH is consulted for a matching command.