// Function Declaration
// 1. Non Parameterized Function and no return 
function greeting(){
  console.log("Hello World JavaScript");
}
greeting(); //Function calling

// 2. Parameterized Function with no return statement and no defaul tvalue
function greet(firstName, lastName){
  console.log("Hello "+firstName+" "+lastName);
}
// If no parameter is passed from the calling statement then the argument(s) are undefined
greet();
function greet(firstName, lastName){
  console.log("Hello "+firstName+" "+lastName);
}
greet("Animesh", "Gaur");
// 3. Parameterized Function and return  
function greet(firstName, lastName){
  return firstName+" "+lastName;
}
console.log(greet("Junaid","Ahmed")); //Function calling
// 4. Parameterized Function and return  and default value
function greet(firstName = "Tina", lastName="Dabi"){
  return firstName+" "+lastName;
}
console.log(greet());
console.log(greet("Junaid","Ahmed")); //Function calling

// Passing function as first class objects
const square = greet;
console.log(square);

// Anonymous functions
const cube = function(x=7){
  return x*x*x;
}
console.log(cube(5));
console.log(cube);

// IMMEDIATELY INVOCABLE FUNCTION EXPRESSION - IIFEs
// 1.Without parameter IIFEs
(function(){
  console.log("IIFE Without any parameter ran...");
  })();
// 2.With parameter IIFEs
(function(name){
  console.log(name);
  })("IIFE With name parameter ran...");
  
  // PROPERTY MEATHODS
  const todo={
    // defining meathods in "todo" variable
    add: function(){
      console.log("Add function in \"var\" running");
    },
    edit: function(id){
      console.log(`Edit function in "var" wirth parameter id = ${id}`);
    }
  }
  // we can alos define a function for todo outside its scope
  todo.del=function(){
      console.log("Del function in \"var\" running declared outside parent scope of todo");
    
  }
  todo.add();
  todo.edit(15);
  todo.del();
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About Javascript

Javascript(JS) is a object-oriented programming language which adhere to ECMA Script Standards. Javascript is required to design the behaviour of the web pages.

Key Features

  • Open-source
  • Just-in-time compiled language
  • Embedded along with HTML and makes web pages alive
  • Originally named as LiveScript.
  • Executable in both browser and server which has Javascript engines like V8(chrome), SpiderMonkey(Firefox) etc.

Syntax help

STDIN Example

var readline = require('readline');
var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
  terminal: false
});

rl.on('line', function(line){
    console.log("Hello, " + line);
});

variable declaration

KeywordDescriptionScope
varVar is used to declare variables(old way of declaring variables)Function or global scope
letlet is also used to declare variables(new way)Global or block Scope
constconst is used to declare const values. Once the value is assigned, it can not be modifiedGlobal or block Scope

Backtick Strings

Interpolation

let greetings = `Hello ${name}`

Multi line Strings

const msg = `
hello
world!
`

Arrays

An array is a collection of items or values.

Syntax:

let arrayName = [value1, value2,..etc];
// or
let arrayName = new Array("value1","value2",..etc);

Example:

let mobiles = ["iPhone", "Samsung", "Pixel"];

// accessing an array
console.log(mobiles[0]);

// changing an array element
mobiles[3] = "Nokia";

Arrow functions

Arrow Functions helps developers to write code in concise way, it’s introduced in ES6.
Arrow functions can be written in multiple ways. Below are couple of ways to use arrow function but it can be written in many other ways as well.

Syntax:

() => expression

Example:

const numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
const squaresOfEvenNumbers = numbers.filter(ele => ele % 2 == 0)
                                    .map(ele => ele ** 2);
console.log(squaresOfEvenNumbers);

De-structuring

Arrays

let [firstName, lastName] = ['Foo', 'Bar']

Objects

let {firstName, lastName} = {
  firstName: 'Foo',
  lastName: 'Bar'
}

rest(...) operator

 const {
    title,
    firstName,
    lastName,
    ...rest
  } = record;

Spread(...) operator

//Object spread
const post = {
  ...options,
  type: "new"
}
//array spread
const users = [
  ...adminUsers,
  ...normalUsers
]

Functions

function greetings({ name = 'Foo' } = {}) { //Defaulting name to Foo
  console.log(`Hello ${name}!`);
}
 
greet() // Hello Foo
greet({ name: 'Bar' }) // Hi Bar

Loops

1. If:

IF is used to execute a block of code based on a condition.

Syntax

if(condition){
    // code
}

2. If-Else:

Else part is used to execute the block of code when the condition fails.

Syntax

if(condition){
    // code
} else {
    // code
}

3. Switch:

Switch is used to replace nested If-Else statements.

Syntax

switch(condition){
    case 'value1' :
        //code
        [break;]
    case 'value2' :
        //code
        [break;]
    .......
    default :
        //code
        [break;]
}

4. For

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
//code  
}

5. While

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
  // code 
}

6. Do-While

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
  // code 
} while (condition);

Classes

ES6 introduced classes along with OOPS concepts in JS. Class is similar to a function which you can think like kind of template which will get called when ever you initialize class.

Syntax:

class className {
  constructor() { ... } //Mandatory Class method
  method1() { ... }
  method2() { ... }
  ...
}

Example:

class Mobile {
  constructor(model) {
    this.name = model;
  }
}

mbl = new Mobile("iPhone");