When working with child processes in Node.js, it is often necessary to determine the exit status or code of the child process. The exit status indicates whether the child process completed successfully or if an error occurred. In this blog post, we will explore how to determine the exit status or code of a child process in Node.js.

Table of Contents

1. The child_process Module
   • Spawning a Child Process
2. Determine Exit Status/Code
   • Using the exitCode Property
   • Using the on('exit') Event
3. Conclusion

The child_process Module

The child_process module in Node.js provides functionality for working with child processes. It allows us to spawn new processes, interact with them, and capture their output.

Spawning a Child Process

To spawn a child process, we can use the spawn() method provided by the child_process module. Here’s an example:

const { spawn } = require('child_process');

const childProcess = spawn('ls', ['-l']);

childProcess.stdout.on('data', (data) => {
  console.log(`stdout: ${data}`);
});

childProcess.stderr.on('data', (data) => {
  console.error(`stderr: ${data}`);
});

childProcess.on('close', (code) => {
  console.log(`child process exited with code ${code}`);
});

In the above example, we are spawning a child process to execute the ls -l command. We attach event listeners to capture the child process’s stdout, stderr, and the close event, which is emitted when the child process exits.

Determine Exit Status/Code

There are multiple ways to determine the exit status or code of a child process in Node.js. Let’s explore two common approaches.

Using the exitCode Property

After a child process exits, Node.js sets the exitCode property on the child process object. We can use this property to determine the exit code. Here’s an example:

const { spawn } = require('child_process');

const childProcess = spawn('ls', ['-l']);

childProcess.on('close', (code) => {
  if (code === 0) {
    console.log('Child process completed successfully');
  } else {
    console.error('Child process exited with error');
  }
});

In the above example, we check the code value passed to the close event listener. If the code is 0, it means the child process completed successfully. Any other value indicates an error occurred.

Using the on('exit') Event

Another way to determine the exit status or code of a child process is by listening to the exit event. This event is emitted when the child process exits and provides the exit code as an argument. Here’s an example:

const { spawn } = require('child_process');

const childProcess = spawn('ls', ['-l']);

childProcess.on('exit', (code) => {
  if (code === 0) {
    console.log('Child process completed successfully');
  } else {
    console.error('Child process exited with error');
  }
});

In the above example, the exit event is used instead of the close event to determine the exit code.

Conclusion

Determining the exit status or code of a child process in Node.js is essential for handling errors and ensuring the proper execution of your application. In this blog post, we explored two common ways to determine the exit status or code using the child_process module. By leveraging these techniques, you can effectively handle child processes and build robust Node.js applications.

#Nodejs #ChildProcess