Child Processes

Node.js can start other processes using the child_process module.

This is useful when you need to run an external command or separate program.

Example use cases

• run a shell command,
• call a Python script,
• process media with FFmpeg,
• run build tools,
• isolate work in another process.

exec vs spawn

exec is useful for simple commands with buffered output.

import { exec } from 'node:child_process'

exec('node --version', (error, stdout) => {
  if (error) throw error
  console.log(stdout)
})

spawn is better for long-running commands or streaming output.

import { spawn } from 'node:child_process'

const child = spawn('node', ['--version'])

child.stdout.on('data', (chunk) => {
  console.log(chunk.toString())
})

Security warning

Never pass raw user input into shell commands.

Bad:

exec(`convert ${userInput}`)

This can cause command injection.

Validate input and avoid shell execution when possible.

Interview answer

Child processes let Node.js run external commands or separate programs. exec is useful for simple buffered commands, while spawn is better for streaming or long-running processes. User input must be handled carefully to avoid command injection.