I recently read about ES6 const keyword and I can understand its importance when having something like this:
(function(){
const PI = 3.14;
it is a common misconception around the web, CONST doesn't creates immutable variables instead it creates immutable binding.
eg.
const temp1 = 1;
temp1 = 2 //error thrown here.
But
temp1.temp = 3 // no error here. Valid JS code as per ES6
so const creates a binding to that particular object. const assures that variable temp1 won't have any other object's Binding.
Now coming to Object. we can get immutable feature with Object by using Object.freeze
const temp3 = Object.freeze( {a:3,b:4})
temp3.a = 2 // it wont update the value of a, it still have 3
temp3.c = 6 // still valid but wont change the object