NodeJS

Question 1

How to access environment variables

Answer 1

process.env.USER_ID;

Question 2

Print stack trace to a console

Answer 2

console.trace()

Question 3

Start and stop timer, print time to the console

Answer 3

console.time("doSomething()");
console.timeEnd("doSomething()");

Question 4

Create path object from a string

Answer 4

const parsed = path.parse("/users/john/project/file.txt")

Question 5

Get filename from "/etc/test/file.txt (file.txt)

Answer 5

path.basename("/etc/test/file.txt")

Question 6

Create path string from components [\_\_dirname, "test", "hello.html"]

Answer 6

path.join(\_\_dirname, "test", "hello.html")

Question 7

Remove obsolete ../ from "/users/joe/..//test.txt"

Answer 7

path.normalize("/users/joe/..//test.txt");

Question 8

How to use async fs methods

Answer 8

import fs from "node:fs/promises";

Question 9

Write or read entire file having fh handle ready

Answer 9

await fh.writeFile("Overwrite content");

const content = await fh.readFile({ encoding: "utf8" });

Question 10

Get user home directory

Answer 10

import os from "node:os";
os.homedir();

Question 11

Create URL object from a string, what you need to import

Answer 11

const myUrl = new URL( "http://mywebsite.com:5000/hello.html?id=100&status=active" )

Nothing to import, it is global constructor

Question 12

What is nodeJS Event Emitter, how to use it (what to import, sample code)

Answer 12

Built-in observer pattern implementation,

import EventEmitter from "node:events";

const eventEmitter = new EventEmitter();

eventEmitter.on("start", (start, end) => console.log("started"));
eventEmitter.emit("start", 1, 100); // Can use any string for event identification

Question 13

Create empty Buffer of 1024 bytes.

Answer 13

const buf = Buffer.alloc(1024);

Question 14

Create Buffer from string Hey

Answer 14

const buf = Buffer.from("Hey!");

Question 15

Access first byte of a Buffer

Answer 15

buf[0];

Question 16

How to force NodeJS production mode

Answer 16

NODE_ENV=production

Question 17

Read file handle fh line by line and print each line.

Answer 17

fh.readLines() returns an async iterable so we need to use for await loop!

for await (const line of fh.readLines()) {
  console.log(line);
}

Question 18

Open file (get fh) in write mode

Answer 18

const fh = await fs.open("temp.txt", "w");

Question 19

Convert Buffer buf to UTF-8 string

Answer 19

buf.toString();

Question 20

What are Streams in NodeJS, give sample streams in NodeJS API

Answer 20

• All streams are instances of EventEmitter, can use events to read and write data.
• Streams process data in chunks, significantly reducing memory usage.

Sample streams:
- fs.ReadStream
- http.IncomingMessage when reading HTTP requests.
- process.stdin
- fs.WriteStream
- process.stdout
- process.stderr

Question 21

How to create a pipeline with streams (like linux readableSrc | t1 | t2 | final). Show both methods

Answer 21

pipe - legacy

readableSrc.pipe(t1).pipe(t2).pipe(final);

pipeline This method is a safer and more robust way to pipe streams together, handling errors and cleanup automatically.

pipeline(readStream, upper, writeStream, (err) => {
  if (err) {
    return console.error("Pipeline error:", err.message);
  }
  console.log("Pipeline succeeded");
});
// In case of error, all streams will be closed.

Question 22

What is backpressure in nodejs streams

Answer 22

Backpressure (Buffering)

• When using streams, it is important to make sure the producer doesn’t overwhelm the consumer.
• For this, the backpressure mechanism is used in all streams in the Node.js API, and implementors are responsible for maintaining that behavior.
• In any scenario where the data buffer has exceeded the highWaterMark or the write queue is currently busy, .write() will return false.
• When a false value is returned, the backpressure system kicks in. It will pause the incoming Readable stream from sending any data and wait until the consumer is ready again.
• Once the data buffer is emptied, a 'drain' event will be emitted to resume the incoming data flow.