doc: child_process.SpawnSync output, stdout, stderr can be null

[manuel-mauky]

📗 API Reference Docs Problem

• Version: v13.9.0
• Platform: Mac OS 10.15.4
• Subsystem: child_process

Location

Section of the site where the content exists

Affected URL(s):

• https://nodejs.org/api/child_process.html#child_process_child_process_spawnsync_command_args_options

Problem description

Concise explanation of what you found to be problematic

In the "Returns" desciption it states that "stdout" and "stderr" can be <Buffer> or <string> and that "output" is of type <Array>.

However, this is not the case when the spawned process terminates with an error.
To reproduce you can run the following script:

const child_process = require("child_process")

// any command that is not available or fails with an error
const result = child_process.spawnSync("not_found") 

console.log(result)

will output:

{
  error: Error: spawnSync not_found ENOENT
      at Object.spawnSync (internal/child_process.js:1045:20)
      ...
    errno: -2,
    code: 'ENOENT',
    syscall: 'spawnSync not_found',
    path: 'not_found',
    spawnargs: []
  },
  status: null,
  signal: null,
  output: null,
  pid: 36085,
  stdout: null,
  stderr: null
}

As you can see "stdout", "stderr" and "output" are null.
I'm not sure if this is a bug in the implementation or if this is the desired behavior. In the latter case it should be stated in the docs that these three fields can also be null and under which conditions this is the case.

---

• I would like to work on this issue and submit a pull request.

[meglio]

This is still a problem for me in 16.2, installed via nvm in MacOS Big Sur.

spawnSync with no options successfully catches stdout and stderr.

spawnSync with a single option, e.g. {env}, returns an object with status, signal, output, stdout, and stderrall set tonull`.

[eherozhao]

I am also seeing this issue with 16.14. My spawnSync is running a command with longer time and nothing print out.