`process.env` is missing environment variables with numeric names

[dpaoliello]

Version

25.2.1, 24.11.1

Platform

Windows 11: Microsoft Windows NT 10.0.28000.0 x64
Ubuntu 24: Linux 6.6.87.1-microsoft-standard-WSL2 #1 SMP PREEMPT_DYNAMIC Mon Apr 21 17:08:54 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

Subsystem

No response

What steps will reproduce the bug?

1. Set an environment variable with a numeric name.
2. Run node.
3. Check in process.env for that environment variable.

For example, in a Windows Command Prompt:

echo console.log(process.env['386']);console.log(process.env['OTHER']); > test.js
set 386=1
set OTHER=1
node test.js

Produces:

undefined
1

I'm not 100% sure how to set such env vars in bash, but it does repro using PowerShell in Ubuntu:

PS> $env:OTHER=1
PS> $env:386=1
PS> node test.js
undefined
1

How often does it reproduce? Is there a required condition?

100% repro.

What is the expected behavior? Why is that the expected behavior?

The environment variable should be present in process.env - a numeric name is valid and can be set once in Node.

What do you see instead?

The environment variable is missing.

Additional information

No response

[targos]

Not Windows-specific.

Also interesting. If there is a numeric variable, process.env becomes impossible to inspect:

> process.env
Uncaught TypeError: Cannot read properties of undefined (reading 'value')
    at formatProperty (node:internal/util/inspect:2532:12)
    at formatRaw (node:internal/util/inspect:1428:9)
    at formatValue (node:internal/util/inspect:1183:10)
    at inspect (node:internal/util/inspect:409:10)
    at REPLServer.writer (node:repl:192:25)
    at finish (node:repl:933:34)
    at finishExecution (node:repl:540:9)
    at REPLServer.defaultEval (node:repl:629:9)
    at bound (node:domain:433:15)

[richardlau]

Also interesting. If there is a numeric variable, process.env becomes impossible to inspect:

That one at least appears to be a regression?

⬢ [rlau@rlau-dev ~]$ env 381=1 ~/.nvm/versions/node/v20.19.5/bin/node
Welcome to Node.js v20.19.5.
Type ".help" for more information.
> process.env
{
  PWD: '/home/rlau',
  HOME: '/home/rlau',
  LANG: 'C.UTF-8',
  NVM_DIR: '/home/rlau/.nvm',
  TERM: 'xterm',
  ...
  PATH: '/home/rlau/.local/bin:/home/rlau/bin:/usr/lib64/ccache:/usr/local/bin:/usr/bin',
  _: '/usr/bin/env',
  '381': undefined
}
>
⬢ [rlau@rlau-dev ~]$ env 381=1 ~/.nvm/versions/node/v24.8.0/bin/node
Welcome to Node.js v24.8.0.
Type ".help" for more information.
> process.env
{
  PWD: '/home/rlau',
  HOME: '/home/rlau',
  LANG: 'C.UTF-8',
  NVM_DIR: '/home/rlau/.nvm',
  TERM: 'xterm',
  ...
  PATH: '/home/rlau/.local/bin:/home/rlau/bin:/usr/lib64/ccache:/usr/local/bin:/usr/bin',
  _: '/usr/bin/env',
  '381': undefined
}
>
⬢ [rlau@rlau-dev ~]$ env 381=1 ~/sandbox/github/node/out/Release/node
Welcome to Node.js v26.0.0-pre.
Type ".help" for more information.
> process.env
Uncaught TypeError: Cannot read properties of undefined (reading 'value')
    at formatProperty (node:internal/util/inspect:2532:12)
    at formatRaw (node:internal/util/inspect:1428:9)
    at formatValue (node:internal/util/inspect:1183:10)
    at inspect (node:internal/util/inspect:409:10)
    at REPLServer.writer (node:repl:192:25)
    at finish (node:repl:933:34)
    at finishExecution (node:repl:540:9)
    at REPLServer.defaultEval (node:repl:629:9)
    at bound (node:domain:433:15)
>
⬢ [rlau@rlau-dev ~]$ 

[targos]

Fix in #60826