execFile for running executables in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of execFile with callback

What will be logged to the console when this Node.js code runs?

Node.js

import { execFile } from 'node:child_process';

execFile('node', ['-e', 'console.log("Hello from execFile")'], (error, stdout, stderr) => {
  if (error) {
    console.error('Error:', error.message);
    return;
  }
  if (stderr) {
    console.error('Stderr:', stderr);
    return;
  }
  console.log('Output:', stdout.trim());
});

A Output: Hello from execFile

B Error: spawn node ENOENT

C Stderr: Hello from execFile

D Output: undefined

💡 Hint

Look at how execFile runs the node executable with inline code and how stdout is handled.

The execFile runs the node executable with the inline script printing 'Hello from execFile'. The callback receives stdout with that output. No error or stderr occurs.

❓ component_behavior

intermediate

Behavior when executable path is incorrect

What happens when execFile is called with a non-existent executable path?

Node.js

import { execFile } from 'node:child_process';

execFile('/path/to/nonexistent', [], (error, stdout, stderr) => {
  if (error) {
    console.log(error.code);
  } else {
    console.log('No error');
  }
});

A ENOENT

B EACCES

C No error

D TypeError

💡 Hint

ENOENT means file or directory not found.

When the executable path does not exist, execFile returns an error with code 'ENOENT' indicating the file was not found.

🔧 Debug

advanced

Why does execFile callback never run?

Consider this code snippet. Why might the callback never be called?

Node.js

import { execFile } from 'node:child_process';

const child = execFile('node', ['-e', 'setTimeout(() => console.log("done"), 1000)']);

// No callback provided

console.log('Script finished');

A The child process never starts without a callback

B execFile requires a callback to run the child process

C The child process runs but output is not captured or logged

D Callback is missing, so no code runs after child process ends

💡 Hint

execFile can run without a callback but output won't be handled.

Without a callback, execFile runs the child process but does not capture or log its output. The callback is optional.

📝 Syntax

advanced

Correct usage of execFile with options

Which option correctly runs execFile with arguments and options to set working directory?

A execFile('ls', (err, stdout) => { console.log(stdout); }, ['-l'], { cwd: '/tmp' });

B execFile('ls', { cwd: '/tmp' }, ['-l'], (err, stdout) => { console.log(stdout); });

C execFile('ls', ['-l'], (err, stdout) => { console.log(stdout); }, { cwd: '/tmp' });

D execFile('ls', ['-l'], { cwd: '/tmp' }, (err, stdout) => { console.log(stdout); });

💡 Hint

Check the order of arguments: executable, args array, options object, callback.

execFile expects the arguments array as second, options object third, and callback last. Only option D follows this order.

🧠 Conceptual

expert

Why prefer execFile over exec for running executables?

Which reason best explains why execFile is preferred over exec when running executables directly?

A execFile supports streaming output, exec buffers all output in memory

B execFile does not spawn a shell, so it avoids shell injection risks and is more efficient

C execFile automatically retries on failure, exec does not

D execFile can run scripts without specifying the interpreter, exec cannot

💡 Hint

Think about security and performance differences between exec and execFile.

execFile runs the executable directly without a shell, reducing risk of shell injection and improving performance. exec runs commands inside a shell.