Common misconception, const only disallows reassignment. For instance,

const number = 1337;

number = 10; // fails

But objects/arrays are not immutable in js, so you can do this:

const person = { name: 'Dude' };

person.name = 'Dudette';

Which is perfectly valid. If you want full immutability, i recommend you check out https://facebook.github.io/immutable-js/, been running it in production, a real pleasure to work with.