So far most of \"starter boilerplates\" and some posts about react / redux I\'ve seen encourage usage of immutable.js to address mutability. I personally rely on Object.as
immutable.js gives you a lot of utilities that always return a new object.
example:
var Immutable = require('immutable');
var map1 = Immutable.Map({a:1, b:2, c:3});
var map2 = map1.set('b', 50);
map1.get('b'); // 2
map2.get('b'); // 50
For just react / redux I personally think that Object.assign is powerful enought, but in some cases the use of that library could save you a few lines of code.