ES6 refers to version 6 of the ECMA script programming language. … is a major extension of the JavaScript language, and adds many more features aimed at simplifying large-scale software development. ECMAScript, or ES6, was published in June 2015. It was later renamed ECMAScript 2015.

Variable:

1. Here are 3 ways to declare a JavaScript variable:

• Var
• Let
• Const

A variable is a container for storing data

Below is how to declare a variable:

Example:

• var: var keyword is a global scope variable declared.

var year=20;
    console.log(name,year);
    console.log(name,year);

• var: Let: The keyword let declare a block scope variable. It is confined within the scope. The variable cannot be re-declared with let, but its value can be changed.

Example:1

let name = "Rukon";
let name= "Delwar";
// SyntaxError: 'x' has already been declared

Example:2

 
{
    let number = 2;
}
    console.log(number)
    // x can NOT be used here

Example:3

Let number=100;
   number=200;
   console.log(number); // number is 200

• Const: The const keyword declares a JavaScript variable with a constant value. Constants are like let variables, values ​​cannot be changed. With const Declared variable blocks have scope.

Example: 1

 
var a = 10;
    
    {
    const a = 2;
    }
    
    console.log(a) // output= 10

Example: 2

const number = 1000;
      number = 122; // This will give an error
      number = number + 10; // This will also give an error

Default parameters:

• The default function allows the parameters named parameters to start with the default value if there is no value or unspecified pass.

Example:

function multiply(a, b = 1) {
                return a * b;
              }
   console.log(multiply(5, 2));
   // expected output: 10
   console.log(multiply(5));
   // expected output: 5

Template string:

• Template use back-tick () instead of quotes ("") to define a string.

Example: 1

let template = `Template string`;

In Template Literal, both single and double quotes can be used inside a string.

Example: 2

let text = `I am "rukon"`;

• The template allows literally multi line strings

Example: 3

let text = `The template allows literally multiline strings`;

• Template literals provide an easy way to expand variable expressions into strings. This method is called string interpolation.

Example: 4

let name= "Rukon";
let year= 20;
let person= `my name is ${name}.I am ${year}!years old`;
console.log(person)

Spread Operator:

• The JavaScript spread operator (…) can copy all data from an existing array or object to another array or object.

Example:

const numbersOne = [1, 2, 3];
const numbersTwo = [4, 5, 6];
const numbersCombined = […numbersOne, …numbersTwo];
console.log(numbersCombined) // outpot 1, 2, 3,4, 5, 6
                        

Arrow Functions:

• The arrow function allows us to write the short function syntax:

We used to write functions like this:

Example:1

Function before() {
    return "Before Function!";
}
console.log(before)

Arrow Function:

Example:2

const arrow = () => {
    return "Arrow Function!";
}
console.log(arrow())

• If the function does not need to be a parameter and returns a single value, then the direct function can be written without a cursor. Then the function becomes smaller.



Example:3

const arrow = () => "Arrow Function";