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;
             }