[BUG] npx/npm exec allows prompt to overwrite output

[bbrk24]

Is there an existing issue for this?

• I have searched the existing issues

This issue exists in the latest npm version

• I am using the latest npm

Current Behavior

When running a script that writes to stdout using fs.write or its relatives via npx or npm exec, the terminal prompt overwrites any output after the last newline (or all output, if no newline was written). See DanielXMoore/Civet#1424 for the discussion and troubleshooting that led to us realizing this is npm's fault.

Expected Behavior

The terminal prompt should be written after the text, not over top of it

Steps To Reproduce

1. Put this script in a .mjs file:

   import { writeSync } from 'node:fs'
   const buf = Buffer.alloc(1, 0x61)
   writeSync(1, buf, 0, 1)

2. Use npx or npm exec to cause this script to be executed
3. Notice that the prompt is written over top of the "a", causing the output to be deleted.

Environment

• npm: 10.9.0
• Node.js: 20.18.0
• OS Name: Ubuntu 22.04 running in WSL 2 on Windows 11
• npm config:

; "user" config from /home/bbrk24/.npmrc

//registry.npmjs.org/:_authToken = (protected)

; node bin location = /home/bbrk24/.nvm/versions/node/v20.18.0/bin/node
; node version = v20.18.0
; npm local prefix = /home/bbrk24/workspace/template-qdeql
; npm version = 10.9.0
; cwd = /home/bbrk24/workspace/template-qdeql
; HOME = /home/bbrk24
; Run `npm config ls -l` to show all defaults.

[reggi]

Given the following project:

#!/usr/bin/env node
import { writeSync } from 'node:fs'
const buf = Buffer.alloc(1, 0x61)
writeSync(1, buf, 0, 1)

{
    "name": "example-7821",
    "bin": {
        "example-7821": "index.mjs"
    },
    "scripts": {
        "start": "node index.mjs"
    }
}

A workaround is to use -s to silent npm's output.

➜  7821 node index.mjs 
a%
➜  7821 npm -s start
a%
➜  7821 npm i . -sg  && npx -s example-7821
a%
➜  7821 npm -s exec . -- start
a%

It's not safe to assume npm won't log or disrupt the expectations of stdout and stderr for any given script. If you need finely tuned output -s is the best bet at ensuring that your script will write to stdout / stderr correctly. Ideally you wouldn't need to add -s in some of these cases, but given that people can have custom log levels, you'd need to use -s to overwrite individual configs anyway.