Child process exit codes in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the exit code of a child process that ends normally?

Consider a Node.js child process that runs a script which completes without errors. What exit code will the child process emit?

Node.js

const { spawn } = require('child_process');
const child = spawn('node', ['-e', 'console.log("done")']);
child.on('exit', (code) => {
  console.log('Exit code:', code);
});

A Exit code: 1

B Exit code: null

C Exit code: 0

D Exit code: undefined

💡 Hint

Normal completion usually returns zero as exit code.

When a child process finishes successfully without errors, it exits with code 0. This is a standard convention indicating success.

❓ Predict Output

intermediate

What exit code does a child process emit if terminated by signal SIGTERM?

If a Node.js child process is killed by the SIGTERM signal, what will be the exit code value received in the 'exit' event?

Node.js

const { spawn } = require('child_process');
const child = spawn('node', ['-e', 'setTimeout(() => {}, 10000)']);
child.on('exit', (code, signal) => {
  console.log('Exit code:', code);
  console.log('Signal:', signal);
});
child.kill('SIGTERM');

A Exit code: null, Signal: SIGTERM

B Exit code: 143, Signal: null

C Exit code: 1, Signal: SIGTERM

D Exit code: 0, Signal: null

💡 Hint

When a process is terminated by a signal, exit code is null and signal is set.

If a child process is terminated by a signal like SIGTERM, the exit code is null and the signal name is provided instead.

❓ component_behavior

advanced

How does Node.js child process handle exit codes on Windows vs Unix?

Which statement correctly describes the difference in exit code behavior of Node.js child processes on Windows compared to Unix-like systems?

A Both Windows and Unix treat exit codes identically with no difference.

B On Unix, exit codes are always positive; on Windows, exit codes can be negative for signals.

C Windows uses signals for exit codes; Unix uses only numeric codes.

D On Windows, exit codes are always positive integers; on Unix, codes greater than 127 indicate signals.

💡 Hint

Unix systems use exit codes greater than 127 to indicate signals, Windows does not.

Unix systems use exit codes greater than 127 to indicate termination by signals, while Windows only uses positive integers for exit codes.

🔧 Debug

advanced

Why does this child process exit event show code null and signal null?

Examine the code below. The child process exits but both code and signal are null. What is the most likely cause?

Node.js

const { spawn } = require('child_process');
const child = spawn('node', ['-e', 'process.exit()']);
child.on('exit', (code, signal) => {
  console.log('Exit code:', code);
  console.log('Signal:', signal);
});

A The child process exited normally with code 0, but code is incorrectly logged as null.

B The child process was terminated by a signal, but signal name is missing.

C The child process called process.exit() without an argument, so code is null.

D The child process did not exit properly, causing both code and signal to be null.

💡 Hint

process.exit() with no argument defaults to exit code 0.

Calling process.exit() without an argument exits with code 0. The exit event should receive code 0, so code being null indicates a logging or event handling mistake.

🧠 Conceptual

expert

What is the meaning of exit code 130 in a Node.js child process?

A Node.js child process exits with code 130. What does this code represent?

A The process completed successfully with warnings.

B The process was terminated by SIGINT (Ctrl+C).

C The process was terminated by SIGTERM.

D The process crashed due to an uncaught exception.

💡 Hint

Exit code 130 is 128 + signal number for SIGINT.

Exit code 130 means the process was terminated by signal 2 (SIGINT). Exit codes for signals are 128 plus the signal number.