Node.js basics

I recently learnt about node.js so thought why not share my learnings?

Here is the basic fundamentals for an absolute beginners of node.js which can be helpful to make a CLI app

1. Command Line Interface (CLI): 🤓

👉If you are writing a program via command line(Black background with text) then it is a CLI(Command Line Interface)

👉 User talk to program via command line is basically CLI

2. Universal rule: 🤓

👉Programming is nothing but input>> processing>> output .

👉Meaning is every program is divided into three parts.

👉Input

👉Processing

👉Output

3. How to get output or print in node.js ? 🤓

console.log("Hello world");

Output 👇

Hello world

4. What is a String: 🤓

Basically,there are total seven primitive data type:

• String
• Number
• Bigint
• Boolean
• Undefined
• Symbol
• Null

👉So,String is one of them which is basically a texual content enclosed in single/double quotation marks

console.log("**I am Samyak Shah**");

5. Variable: 🤓

Variable: A placeholder for storing the information and whenever required,we can take it from them.

👉For example we assume a study table(placeholder) on which we put pen,pencil,calender,lamp etc. So things are stored in placeholder,whenever required,we will get it from them by defining it.

var myName = "Samyak";
console.log(myName);

Output 👇

Samyak

6. String Concatenation: 🤓

👉String Concatenation: Suppose we have one variable: myName in which "Samyak" is stored. Say We have to welcome Samyak. So, console.log("Welcome " + myName); is string concatenation.

var myName = "Samyak"
console.log("Welcome " + myName)

Output 👇

Welcome Samyak

7. Packages: 🤓

👉Packages: A package is a directory with one or more modules inside of it and a package. json file which has metadata about the package.

👉Basically,In programming,we can use code written by others too...thats what package is.

8. How to take input from User in CLI? 🤓

👉To take input from user,in browser we use prompt() while in CLI,we use ReadlineSync npm library

https://www.npmjs.com/package/readline-sync

var readlineSync = require('readline-sync'); //package
 // In repl.it, package is installed automatically
var userName = readlineSync.question("May I have your name? ");
console.log("Hi" + userName + "!");

Output 👇

May I have your name?

// You have to answer it now

Samyak

// final output

Hi Samyak!

9. If else statement: 🤓

👉Branching is usually done with if else. Also note that branching of code, i.e. only one branch runs based on a CONDITION

var readlineSync = require('readline-sync'); //package

var userName = readlineSync.question("Am I older than 25?")

if (userName=== "No"){
  console.log("You are right!")
}else {
 console.log("You are wrong!")
};

Output 👇

// case 1

Am I older than 25? No

You are right!

// case 2

Am I older than 25? Yes

You are wrong!

10. Function : 🤓

👉Know Syntax:

function functionName(parameterOne, parameterTwo) {

  return outputValue;
}

👉Function should be followed by

-The name of the function.

-A list of parameters to the function, enclosed in parentheses and separated by commas.

-Something that defines a function,enclosed in curly brackets.

function **add**(x,y) **{** 
//see curly brackets
//note that add is name of function
// x,y are list of parameters to function enclosed in parentheses and seperated by commas.

var sum = x + y; //processing
return sum; 
**}**
var output = add(3,4); //calling the function
console.log(output)

👉What is return?

When a return statement is used in a function body, the execution of the function is stopped. If specified, a given value is returned to the function caller.

👉What is calling a function?

When you define a function you give a name to a set of actions you want the computer to perform. When you call a function you are telling the computer to run (or execute) that set of actions.

11. Function Parameters and Arguments: 🤓

👉Know about parameters and arguments: 👉Parameters: function functionName(parameterOne, parameterTwo) Bold texts are Function parameters 👉Arguments: function functionName(5,10) The real values passed to function are Function arguments

function functionName(parameterOne, parameterTwo) //function parameters


function functionName(1,2) //function arguments

12. Understanding for loop: 🤓

calling a function from the loop is running the mini-program multiple times: This is nothing but console.log in for loop to get output

//syntax
for (intial CONDITION; exit CONDITION; change CONDITION) {

}

//program
for (let i = 0; i < 3; i++) {
  console.log("Samyak Shah")

}

Output 👇

Samyak Shah

Samyak Shah

Samyak Shah

Note :

👉Initial sets a variable before the loop starts (let i = 0).

👉Exit defines the condition for the loop to run (i must be less than 3).

👉Change increases a value (i++) each time the code block in the loop has been executed.

13. Array: 🤓

👉Data structure is just a way of organizing data in a particular way. In the case of an array, data is arranged sequentially and thus can be accessed using index numbers.

👉Think of the array like contents of a book. You can see what's there in each chapter from the top and directly go to a chapter when you know the page number. All chapters are in a sequence. 👉So exactly like that you can relate to Array

Must know:

👉index-based access, the index starts at 0 not from 1

var listToBuy = ["Pen","Pencil","Eraser"]

14. JavaScript Objects: 🤓

JavaScript Objects:

👉The Object class represents one of JavaScript's data types. It is used to store various keyed collections and more complex entities.

{
key: value;
},

👉 This world is trying to map everyday things to programming concepts.When you think about superman,lets define it: Superman has powers which is to fly,costumecolors which is blue so

power: "Flight"

costumeColors: "Blue"

👉Power and costumeColors are the key and Flight and Blue are the values.

👉Note that different values in datastructures are seprated by comma ( , )

var superman = {
power: "Flight", 
costumeColors: "Blue",
}

How to access these values?

console.log(superman.power) 
// dot accesses the property of superman

Output 👇

Flight

👉Also note that console is an object on which log() is a property. And yes, functions too can be a property of object.

👉When functions are properties of an object, they are called methods in programming.

I hope so far you have gained the learnings for node.js.

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