In Node.js, child processes can be used to run external commands or scripts in a separate process. Often, these child processes might take some time to complete, making it useful to have a progress bar to indicate the progress of the task being executed.

In this blog post, we will explore how to implement a progress bar for child processes in Node.js using the readline module.

Table of Contents

• Setting up the project
• Creating the progress bar
• Updating the progress
• Running the child process
• Summary

Setting up the project

Before we dive into implementing the progress bar, let’s set up a new Node.js project. Create a new directory for the project and navigate to it in your terminal. Then, initialize a new Node.js project by running the following command:

$ npm init -y

Next, install the readline module by running:

$ npm install readline

Creating the progress bar

To create the progress bar, we will use the readline module, which provides an interface for reading lines from a readable stream, such as process.stdout.

Create a new file called progressBar.js and add the following code:

const readline = require('readline');

class ProgressBar {
  constructor(total) {
    this.total = total;
    this.current = 0;
    this.rl = readline.createInterface({
      input: process.stdin,
      output: process.stdout,
    });
  }

  update() {
    this.current++;
    this.rl.clearLine();
    this.rl.cursorTo(0);
    this.rl.write(`Progress: ${Math.round((this.current / this.total) * 100)}%`);
  }

  complete() {
    this.rl.close();
  }
}

module.exports = ProgressBar;

In the ProgressBar class, we initialize the readline interface with process.stdin and process.stdout. The update method is used to update the progress bar by clearing the line, moving the cursor to the beginning of the line, and writing the updated progress percentage. The complete method is used to close the readline interface when the process is complete.

Updating the progress

Next, let’s create a separate file called progressExample.js to demonstrate how to use the progress bar. Add the following code:

const ProgressBar = require('./progressBar');

const totalTasks = 10;
const progressBar = new ProgressBar(totalTasks);

// Simulating a long-running task
function simulateTask() {
  return new Promise((resolve) => {
    setTimeout(resolve, 1000);
  });
}

async function runTasks() {
  for (let i = 0; i < totalTasks; i++) {
    await simulateTask();
    progressBar.update();
  }

  progressBar.complete();
}

runTasks();

In this example, we create a ProgressBar instance, specifying the total number of tasks to be completed. We then define a simulateTask function that returns a promise to simulate a long-running task.

The runTasks function iterates over a given number of tasks, waits for each task to complete using simulateTask, and then updates the progress bar using progressBar.update. Finally, we call progressBar.complete to close the progress bar interface.

Running the child process

To use the progress bar with a child process, we can modify the runTasks function in progressExample.js to execute a child process command. Here’s an example:

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

async function runTasks() {
  for (let i = 0; i < totalTasks; i++) {
    await new Promise((resolve) => {
      exec('some-command', (err) => {
        if (err) {
          console.error(err);
        }
        resolve();
      });
    });

    progressBar.update();
  }

  progressBar.complete();
}

runTasks();

Replace 'some-command' with the command you wish to execute as a child process.

Summary

In this blog post, we learned how to implement a progress bar for child processes in Node.js. We used the readline module to create an interface for updating and displaying the progress bar. The progress bar can be useful for providing feedback and indicating the progress of long-running tasks or child processes.

Remember to install the readline module before running the code. Feel free to customize the progress bar’s appearance and functionality to fit your specific requirements.

#nodejs #progress-bar