Use of object.assign() in chapter 8 about meiosis HOT 1 CLOSED

Excellent points!

You are correct, we are mutating the object, and we have set up a controlled way of re-rendering the view on the same object, using streams to control when the re-rendering occurs.

Later on, when using a stream of functions for updates, the nesting function is:

var nestUpdate = function(update, prop) {
  return function(func) { // this is the nested update. take the incoming func, and
    update(function(model) { // call the original update, and
      model[prop] = func(model[prop]); // call func on the nested model
      return model;
    });
  };
};

Again, we are mutating model and returning it.

The Meiosis pattern works well both with mutation and immutable objects. Because we have set up a clear, unidirectional reactive loop, mutation is unlikely to cause bugs. I did not want to prescribe immutability because it is not required for the pattern to work well.

Object.assign is used to gradually explain the concept of a stream of updates, working our way up to using a stream of functions for updating the model. Once reached, utilities such as Ramda and Lodash-FP can help with producing new objects instead of mutating existing ones. I have sections on these libraries in the Documentation. But again, I don't want to imply that immutability is a requirement.

As you said, there are some functional programming patterns that rely on immutable objects. Indeed I am trying to teach some FP concepts because they are useful with Meiosis, but there's nothing wrong with using mutation.

Thank you for your feedback, I appreciate it!

from meiosis.