ES6

var, let and const keywords-------------------------------------------------
  var lets you override its values
  it can be declared globally or within a function locally
  
  let does not lets you override its code and throws error on trying to do so
  it has local scope
  
  const keyword lets you declare a variable and has 'read-only' property.
  they cannot be reassigned 
  
"use strict"----------------------------------------------------------------
  enables strict mode and watched for common mistakes
  
array declaration using const-----------------------------------------------
  array declared using const are mutable. example:-\
  const s = [2, 3, 4];
  s[1] = 5; //s = [2, 5, 4]
  
freezing objects to prevent mutation----------------------------------------
  to prevent any kind of mutations we use
      Object.freeze(objectname);
      
  example:-
      const things = {apple, cat, ball};
      Object.freeze(things); //no mutation is possible in things
 
creating inline functions / concise anonymous functions---------------------
     to create a concise function we use the following syntax:-
          const afun = function(){
             const aval = "value";
             return aconst;
             }
             
                OR
                
          const afun= () => {
             const aval = "value";
             return aconst;
             }
             
 using the spread operator to compute values--------------------------------
       the spread operator is helpful where a number of argu,ents are expected. 
       Eg:- for calculating the maximum number in an array. using var declaration with apply, math can be tedious and thus spread operator can be useful
             const arr = [ 1, 23, 65, 78];
             const maximum = Math.max(...arr);
             
 using destructive assignment to assign values from objects directly--------
        we can shorten a piece of code to assign values directly from the objects like :-
        const jhon = { age: 30, title: sikle};
        const age = jhon.age;
        const title = jhon.title;
        
        USING DESTRUCTIVE ASSIGNMENT FOR ASSIGNING VALUE
        const jhon = { age: 30, title: sikle};
        const {age, title} = jhon; //does the same as the above code
        
        TO ASSIGN A DIFFERENT VARIABLE NAME 
        const jhon = { age: 30, title: sikle};
        const {age: user_age, title: user_title} = jhon;
        
        TO ASSIGN VALUE FROM A NESTED OBJECT
        const people = { jhon { age:21, title:doe }};
        const {jhon :{ age, title} = people;

using destructive assignment to access the elements of an array-------------
        for assigning values to array directly we can use the variable name
        Eg:-
           const [a, b , , , c] = [1, 2, 3, 4, 5, 6, 7];
           console.log(a, b, c); //1, 2, 6
           
           //for swapping values
           a = 3;
           b = 6;
           [a,b] = [b,a];
           
using destructive assignment with rest parameter---------------------------
      we can use rest parameter and destructive assignment together too
      Eg:-
          const [a,b, ...arr] = [1, 2, 3, 4, 5, 6, 7];
          console.log(a,b); //1, 2
          console.log(...arr); //3, 4, 5, 6, 7
          
writing functions directly using the destructive assignment-----------------
      we can directly assign vales in a function using destructive assigment:-
      Eg:-
         const temp = { min: 10, max: 40, day: 32 };
         const avg_temp = ({ min, max }) => (min + max) / 2.0;
         
creating strings with template litrals--------------------------------------
      template litral helps in  making complex strings easier
      The string should start and end with `  and not '. the assignement is done by ${..}
      Eg:-
         const person = { name: abc, age: 50};
         const greetings = ` Hi everyone , my name is ${person.name}. I am ${person.age} years old.`;
         
writing a concise object declaration with ES6-------------------------------
      rather than writing {x:x, y:y} we can directly assign by writing ({x, y})
      Eg:- 
         person( "abc", 28, "female");
         const person = (name, age, gender) =>  ({ name, age gender})