Njs

Question 1

How do you start to create a program in nodeJs?

Answer 1

npm init

npm init -y

Question 2

How do u install a package in nodeJS?

Answer 2

npm install ws

Question 3

How do u run a nodeJS program?

Answer 3

node index.js

Question 4

What is “g” in,

npm install -g

Answer 4

It installs a package in a globally available system directory. You can find that directory with following command,
npm root -g

It won’t install it in the current project directory. That has to be done again without “-g”.
After this you can install this package even if internet is not available. It will install the package from local system directory.

You may need root access.

Question 5

Give an example of importing a package in nodeJS.

Answer 5

const WebSocket = require(‘ws’);

Question 6

How do you printf from a NodeJs program?

Answer 6

console.log(“Hello World”);

Question 7

How do you catch an event in Node.js

Answer 7

using “on” method of EventEmitter.

eventEmitter.on(“evnt_name”, handlerFunctionName);

Question 8

How do u read a file in nodeJs?

Answer 8

var fs = require('fs');
fs.readFileSync("./filename.txt");

Question 9

What is a good for NodeJs documentation.

Answer 9

www.nodejs.org/api
or
www.nodejs.org -> go to ‘Docs’ tab.

Question 10

what are var, const and let variables in Node.js

Answer 10

var declares a variable.
const declares and defines a variable, that cannot be re-assigned.

let x = 5 defines a variable only at the block level, like a for loop counter etc.

Question 11

Where to look for node.js packages

Answer 11

www.npmjs.com

Question 12

How are constructor defined in nodejs class?

Answer 12

Inside class curly brackets,
constructor(firstName, LastName) { ... }

Question 13

How do you drive a child class from parent class in node.js?

Answer 13

class child_class extends parent_class { … }

Question 14

How do u call constructor of parent class in child class in node.js?

Answer 14

super( parent class parameters);

Question 15

How is event emitted in node.js?

Answer 15

eventEmitter.emit(‘event_name’); // No event parameters
Handle with the function like this,
function event_handler() { … }
Bind event_name and event_handler() as follows,
eventEmitter.on(‘event_name’, event_handler);

If event has parameters, event_handler function should also accept same parameters, see below,

eventEmitter.emit(‘event_name’, event_arg1, event_arg2);
event_handler(event_arg1, event_arg2) { … }

Question 16

How is event emitter is created in node.js?

Answer 16

var events = require('events');
var eventEmitter = nre events.EventEmitter();

eventEmitter.on('event_name', function_name);
eventEmitter.emit('event_name', arg1, arg2);
function function_name(arg1, arg2) { ... }

Question 17

How is util package used to make a child_class inherit a parent_class in node.js?

Answer 17

var util = require('util');
util.inherits(child_class, parent_class);

This can be used to make a class event emitter
var events = require('events');
util.inherits(child_class, events.EventEmitter);

Question 18

How to add time delay in a NodeJs program?

Answer 18

npm install sleep
var sleep = require("sleep");
sleep.sleep(5);  // 5 second delay

Question 19

How do u access command line args in node.js

Answer 19

process.argv
This will return an array
process variable is available to all node.js programs.

Question 20

How do you access process details in a node.js program

Answer 20

By using “process” variable available to all node.js programs
process.stdout.write(“Hello\n”);
is same as console.log(“hello”);

Question 21

In node.js how to call a function 5 seconds from now?

Answer 21

function func1() {...}
setTimeout(func1, 5000)

Question 22

In node.js, How to call a function repeatedly every 3 seconds?

Answer 22

setInterval(func1, 3000);

Question 23

How to exit a node.js program at any place in code?

Answer 23

process.exit();

Question 24

In node.js, what package is needed to create a UDP socket?

Answer 24

const dgram = require('dgram');
const client_skt = dgram.createSocket('udp4');
const srvr_skt = dgram.createSocket('udp4');

Question 25

How to create a buffer from a string in node.js?

Answer 25

var buf = new Buffer.from(“ABCD”);

Question 26

How to create a buffer of a specified length in node.js?

Answer 26

var buf = Buffer.alloc(15);

Question 27

How do u write a string to a buffer in node.js?

Answer 27

var bfr = Buffer.alloc(256);
len = bfr.write("ABCD");
len is octets written.

Question 28

Give example of a map in node.js

Answer 28

var sqrs = new Map([ [7, 49], [8, 64], [9, 81] ]);

Question 29

In node.js, how to read a file line by line?

Answer 29

use package line-by-line.
const  lineReader = require('line-by-line');
lr = lineReader('file_name.txt');
lr.on('line', function(txt) {// txt is a full line});
lr.on('end', function(){// end of file reached});
lr.on('error', function(err){print err});

Question 30

In node.js, how to call functions defined in another js file?

Answer 30

// math.js
function add(x, y) {return x+y;}
function mult(x, y) { return x*y;}
module.exports = {add, mult};

// app.js
var hisaab = require('./math');
m = hisaab.mult(7, 8);
s = hisaab.add(5, 7);

Question 31

Give an example of class definition in node.js

Answer 31

class Person{
  constructor(nm){
    this.name = nm;
  }
  printName() {
    console.log(this.name);
  }
}

john = new Person('John Doe');
john.printName();

Question 32

How to find 3rd character in a string name?

Answer 32

name = “Elon”;

console.log(name.charAt(2)); // prints o

Question 33

How to convert an integer to ascii string in node.js?

Answer 33

var num = 217;
var str_rep = num.toString();
console.log(typeof  str_rep);  // prints string

Question 34

How to find the type of an object in node.js?

Answer 34

var age = 29;
console.log(typeof age);  // prints number

var name = "Spock";
console.log(typeof name); // prints string

Question 35

How to concatenate two strings in node.js?

Answer 35

var firstName = "Elon";
var lastName = "  Musk";
var fullName = firstName.concat(lastName);

Question 36

How to declare an arry in node.js?

Answer 36

var names = [];
var cities = ["Delhi", "Washington"];
citiess.push("London");

Question 37

What are node.js objects?

Answer 37

key: value pairs,
value can be a function

var Person = {
  firstName : "Isac",
  lastName : " Newton",
  fullName : function {
   fn = this.firstName.concatenate(this.lastName);
    return fn;
  }
}

Question 38

How to find length of an array in node.js?

Answer 38

var sqr = [1, 4, 9, 16]
sqr.length;

Question 39

How to iterate over an array in node.js?

Answer 39

var arr = [1, 2, 3];
for(let i in arr){
  console.log(arr[i]);
}

Question 40

In node.js, how do you convert an string to a JSON object?

Answer 40

var str = "{\"age\": 47}";
var jsnObj = JSON.parse(str);

To convert JSON obect to string
var str2 = JSON.stringify(jsnObj);

To get length of a JSON array
jsnObj.length;

Question 41

In node.js, how do u split a string?

Answer 41

use string.split(“ “);
str = “aaaaKKbbbbKK123”;
str.split(“KK”); // [“aaaa”, “bbbb”, “123”]

To split a multi-line string into separate lines,
os = require(‘os’);
str = fs.readFileSync(‘file_1.txt’).toString();
lines = str.split(os.EOL);

Question 42

In node.js, how to separate a file content into individual lines synchronously?

Answer 42

os = require('os');
str = fs.readFileSync('file_1.txt').toString();
lines = str.split(os.EOL);

Question 43

How do you get the request type (GET, POST) from a HTTP type in node.js? Also how to retrive POSTed data at the server?

Answer 43

In request handler function, there are two parameters (req, resp). Request type is available in req.method (GET or POST).

Question 44

How to install nodejs on Ubuntu?

Answer 44

For latest procedure, got to www.nodejs.org
–> Downloads –> Debian & Ubuntu …

This directs to github
https://github.com/nodesource/distributions/blob/master/README.md#deb

For version 10.x procedure is,

curl -sL https://deb.nodesource.com/setup_10.x | sudo -E bash -
sudo apt-get install -y nodejs

Question 45

How to update npm to latest version in nodejs?

Answer 45

sudo npm install -g npm

Question 46

nodejs: How to list globally installed packages?

Answer 46

npm list -g

npm list -g –depth=0

Question 47

nodejs: How to un-install a package?

Answer 47

npm uninstall pkg_name

Question 48

nodejs: How to search list of available packages containing a given string?

Answer 48

npm search mkdir

mkdir is string to search in package names.

Question 49

nodejs: How to create a file synchronously, and write to it?

Answer 49

var  fd = fs.openSync("./new_file.txt", "w");
fs.writeSync(fd, "ABCDWXYZ", 0, 9, null);

Question 50

nodejs: How to get string representation of an integer?

Answer 50

var num = 123;
var str = num.toString();

Question 51

nodejs: How to filter out negative numbers from an array?

Answer 51

function isPositive(num) { return num > 0; }
arr = [15, 7, -65, 9, -25];
newArr = arr.filter(isPositive);

Question 52

nodejs: How to remove first element of an array?

Answer 52

use shift()
let cats = [‘Bob’, ‘Willy’, ‘Mini’];
cats.shift(); // [‘Willy’, ‘Mini’]

shift() returns the removed item.

To remove last, item use pop()

Question 53

nodejs: How to check if an array is empty?

Answer 53

if(arr.length > 0) { // Array is not empty }

Question 54

Nodejs: How to find all keys in a json object?

Answer 54

const  jsnStr = "{ ....... }";
var jsnObj = JSON.parse(jsnStr);
var keys = Object.keys(jsnObj);

variable keys will contain an array of all key strings.

Question 55

Nodejs: What is “Object”?

Answer 55

It is some kind of a global object, available everywhere. It has many useful functions built into it, e.g.,
Object.keys()
can be used to find all keys in a json object.
Find out more about it.

Question 56

Nodejs: How to find length of a string?

Answer 56

const str = "ABCDEF";
var len = str.length;

Question 57

Nodejs: what exactly is the difference between __proto__ and prototype?

Answer 57

Find out more about it.

Question 58

Nodejs: how do u throw an exception?

Answer 58

Try {
  throw new Error('error msg');
}
catch(e) {
  console.log(e.message);
}
finally {
  // this will always execute
}

Question 59

Nodejs: How to print variables in a string?

Answer 59

let  var1 = 123;
console.log(`Value of var1 is  ${var1}`);
Note we have used back ticks on left of '1' key.

Question 60

Nodejs: what does Object.create() do?

Answer 60

When u create a new object from an existing one using Object.create(), the new object looks for properties in parent object if it fails to find them in itself.

childObj = Object.create(parentObj);
childObj.prop_A;
if prop_A is not there in childObj, it will be looked in parent.

Question 61

Nodejs: How are global variables implemented internally in NodeJs?

Answer 61

There is a “Global Object”, all global variables are properties or attributes of this object.

Question 62

Nodejs: How are local variables implemented internally in NodeJs?

Answer 62

Each time a function is called, a “Call Object” is created. Each local variable in that function is attribute or property of that “Call Object”.

When using a variable, most recent “Call Object” is searched first for that variable. If this search fails, next most recent “Call Object” is searched, all the way up to “Global Object”.

Question 63

NodeJs: How can you modify some characters in a string?

Answer 63

You can’t really modify a string. They are immutable.

Question 64

NodeJs: What is ‘delete’ used for?

Answer 64

delete is used to remove individual attributes/properties of objects. Not whole objects, which is automatically done by the garbage collector.

Question 65

NodeJs: What is ‘arguments’ object?

Answer 65

Inside a function, arguments object is an array, that contains all arguments passed to that function invocation, even if number of arguments defined is less then called actual arguments.

arguments.length is the total number of arguments passed to this function invocation.