const in js

1. new const feature
   
   in the past there was no real constants in js, everything could be overwritten (even sometimes keywords)
   in ECMAScript6 this has been alleviated
   
   const in JS means the object can be assigned once
   if you try this
   
   const i = 45
   i= 0
   console.log(I)
   
   
   this will fail
   SyntaxError: Identifier 'i' has already been declared
   
   with objects member can be assigned afterwards
   
   
   const obj2 = {}
   obj2.a ="gg"
   
   
   
   but subsequent
   obj2 = {}
   will fail
   
   even with const, the only way to have a readonly member of an object is
   
   var testobj = {};
   Object.defineProperty( testobj , "pseudoconst",
   {
   value: 3,
   
   writable: false,
   
   enumerable: true,
   
   configurable: true
   });
   
   testobj.pseudoconst
   3
   testobj.pseudoconst = 5//this wont raise an error but wont change the value either
   5
   testobj.pseudoconst
   3