Category: JavaScript Answers

Sometimes, we want to copy a file quickly in Node.js.

In this article, we’ll look at how to copy a file quickly in Node.js.

How to copy a file quickly in Node.js?

To copy a file quickly in Node.js, we can use the fs.copyFile method.

For instance, we write

const fs = require('fs');

fs.copyFile('source.txt', 'destination.txt', (err) => {
  if (err) {
    throw err;
  }
  console.log('source.txt was copied to destination.txt');
});

to call copyFile with the path of the file to copy, the path to copy to, and a callback that’s run copyFile is done.

If err is set, that means an error occurred when copying.

Otherwise, the source file has been copied successfully.

Conclusion

To copy a file quickly in Node.js, we can use the fs.copyFile method.

Sometimes, we want to run a Node.js app as a background service.

In this article, we’ll look at how to run a Node.js app as a background service.

How to run a Node.js app as a background service?

To run a Node.js app as a background service, we can use the daemon module.

To install it, we run

npm i daemon

Then we use it by writing

const daemon = require('daemon');

daemon.daemonize({
  stdout: './log.log',
  stderr: './log.error.log'
}, './node.pid', (err, pid) => {
  if (err) {
    console.log(err);
    return process.exit(-1);
  }
  console.log(pid);
});

to call daemon.daemonize with an object with the path for stdout and stderr set to the log file path as the 1st argument.

The 2nd argument is the path to the script we want to run.

The 3rd argument is the callback that runs when daemon.daemonize is done.

If there’s an error, err will be set.

pid is the process ID and it’ll be set when the daemon is started.

Conclusion

To run a Node.js app as a background service, we can use the daemon module.

Sometimes, we want to print a stack trace in Node.js.

In this article, we’ll look at how to print a stack trace in Node.js.

How to print a stack trace in Node.js?

To print a stack trace in Node.js, we can get the stack property from the Error instance.

For instance, we write

const {
  stack
} = new Error()
console.log(stack)

to get the stack trace from the stack property of the Error instance.

We can also use console.trace method with no argument to print the stack trace.

Conclusion

To print a stack trace in Node.js, we can get the stack property from the Error instance.

Sometimes, we want to get the full URL in Express and Node.js.

In this article, we’ll look at how to get the full URL in Express and Node.js.

to get the full URL in Express and Node.js

To get the full URL in Express and Node.js, we can use the url package.

To install it, we run

npm i url

Then we can use it by writing

const url = require('url');

const fullUrl = (req) => {
  return url.format({
    protocol: req.protocol,
    host: req.get('host'),
    pathname: req.originalUrl
  });
}

to define the fullUrl function that takes the Express request req object.

And then we call url.format with an object that has the protocol, host, and pathnameset from the URL components inreq`.

protocol has the protocol like http or ftp.

host has the first segment of the URL after the protocol.

And pathname has the rest of the URL.

Conclusion

To get the full URL in Express and Node.js, we can use the url package.

Sometimes, we want to read a file one line at a time in Node.js.

In this article, we’ll look at how to read a file one line at a time in Node.js.

How to read a file one line at a time in Node.js?

To read a file one line at a time in Node.js, we can call thge fs.createReadStream method.

For instance, we write

const fs = require('fs');
const readline = require('readline');

const processLineByLine = async () => {
  const fileStream = fs.createReadStream('input.txt');
  const rl = readline.createInterface({
    input: fileStream,
    crlfDelay: Infinity
  });

  for await (const line of rl) {
    console.log(`Line from file: ${line}`);
  }
}

processLineByLine();

to define the processLineByLine function that calls fs.createReadStream with the path of the file to read.

Then we call readline.createInterface to read the file line by line by setting the input to fileStream and crlfDelay to Infinity.

crlfDelay is set to recognize all instacnes of the CR and LF characters as a single line break.

And then we loop through each line in rl that’s read.

Conclusion

To read a file one line at a time in Node.js, we can call thge fs.createReadStream method.