JS ES6 Basics

Learn JS ES6 Basics

Published June 22, 2021

JS ES6 Basics

Let keyword
Let keyword Example
Const Keyword
Const Keyword Example
Function Rest Parameter
Function Rest Parameter Example
Arrow Functions
Arrow Functions Example
Javascript classes
Javascript classes Example
Template Literals
Template Literals Example

Let keyword

The let keyword allows you to declare a variable with block scope.

Let keyword Example


var x = 20;
console.log("x outer scope value: "+x);

{
  let x = 10; 
  console.log("x inner Scope with let : "+x);
}

console.log("x outer scope value: "+x);

Const Keyword

The const keyword allows you to declare a constant(an unchangeable value). const is similar to let, except that it’s value cannot be changed.

Const Keyword Example


var x = 20;
console.log("x outer scope value: "+x);

{
  const x = 10;  // Const x means value cannot be changed
  console.log("x inner Scope with let : "+x);
  
  //x =15; // if you try to update with new value it will raise error.
}

console.log("x outer scope value: "+x);

Function Rest Parameter

The rest parameter allows a function to treat an indefinte number of arguments as array.

Function Rest Parameter Example


function sum(...args){

  let result = 0;

  for(let arg of args)
    result +=  arg;

  return result;
}


console.log(sum(5,6));

Arrow Functions

Arrow functions allows a short syntax for writing function expressions. You don’t need the function keyword the return keyword and the curly brackets.

Arrow Functions Example


var x = function (x,y) { return x*y; }

console.log(x(4,3));

const a = (b,c) => b * c;

console.log ( a(4, 3));

Javascript classes

Javascript classes are template for Javasript objects. We can use class keyword to create class. In addition always use a method name constructor() inside the class.

Javascript classes Example


class Rectangle {
  constructor(height, width) {
    this.height = height;
    this.width = width;
  }
  
  get area() {
    return this.calcArea();
  }
  
  calcArea() {
    return this.height * this.width;
  }
  
  
}


var r = new Rectangle(6,6);

console.log( r.calcArea() );

Template Literals

In ES6, you create a template lieteral by wrapping your text in backticks (`) as follows. Template literals are string literals allowing embedded expressions. You can use multi-line strings and string interpolation features with them.

Template Literals Example


let expression = "embeded here";

console.log(`string message`);

console.log(`string message line 1
 string message line 2`);

console.log(`string message ${expression} as string text`);