MobX Quick Start Guide

Fine-tuning primitive types

The single model type that we have seen so far is just the beginning and can barely be called a tree. We can expand the domain-model to make it more realistic. Let's add a User type, who will be creating the todo items:

import { types } from 'mobx-state-tree';const User = types.model('User', {    name: types.string,    age: 42,    twitter: types.maybe(types.refinement(types.string, v =>       /^\w+$/.test(v))),});

There are some interesting details in the preceding definition, as follows:

• The age property has been defined as the constant 42, which translates to a default value for age. When no value is provided for a user, it will be set to this default value. Additionally, MST is smart enough to derive the type to be number ...