Introduction to the newline guide to building a React App with MobX State Tree

Application Overview

State Management on the JavaScript ecosystem

State Management

What is MobX State Tree?

What will you learn in this course?

Will this course be for you?

Introduction

Introduction to the mental model of MobX State Tree

The Tree in MobX State Tree

Introduction to the store model of MobX State Tree

The Store Model

Introduction to the types in MobX State Tree

Types

Introduction to the model actions of MobX State Tree

Model Actions

Introduction to the model views of MobX State Tree

Model Views

Introduction to the store snapshots of MobX State Tree

Snapshots

Identifiers and references of MobX State Tree

Identifiers and References

Asynchronous Actions

Lifecycle Hooks

Concepts

Arrays in MobX State Tree

Maps

Working with nested stores in MobX State Tree

Nesting Stores

Optimistic Updates

Time Travel

Advanced Concepts

Overview of React and MobX State Tree

Combining MobX State Tree with React via Context and a custom Hook

Context and Hooks

Observable

React

Overview

Building Voyager

mobx-state-tree

In this course, we will create a complete React Application with the state management handled by MobX State Tree, a state container system that is built on MobX, a functional reactive state library.

MobX State Tree will give your application a solid structure and foundation for large-scale applications and for small applications that are expected to scale rapidly. In comparison to Redux, MobX State Tree outstands it in performance with much less boilerplate. MobX is one of the most popular Redux alternatives and it's used by companies all over the world, including Netflix, Grow, IBM, DAZN, Baidu, and more.

During this course, you'll learn:

* Types in MobX State Tree.
* How to create the architecture of a centralized store.
* How to mutate the state via actions that could be asynchronous or not, depending on if we need to perform network requests to persist data into a database via GraphQL.
* Understanding snapshots and how we can benefit from them to time-travel if a network request fails.
* Understanding how MobX State Tree makes use of observable properties and observers.
* Leveraging re-renders in your React Application to MobX observers for better performance optimizations.

By the end of this course, you will have the knowledge and skills that it takes to build a real-world, production-level React Application with a State Management with top-notch performance that can scale with ease.

In this course, we'll show you how to build a React App with MobX State Tree.

The newline Guide to Building a React App with MobX State Tree

How to integrate MobX State Tree within your React App

Dealing with asynchronous flows and time travel to preserve state on networking errors

How to create a scalable store using MobX State Tree

---
title: Asynchronous Actions
slug: asynchronous-actions-in-mobx-state-tree
description: Asynchronous Actions in MobX State Tree
role: "LESSON"
isPublicLesson: false
---

# Asynchronous Actions in MobX State Tree

In the JavaScript world and in web application development, it is a common practice to asynchronously fetch data from a server to display in your application user interface. A common way of doing this is with the `async/await` function expression, or with `Promises`, or with `Generators`. In MobX State Tree, you can write asynchronous actions but in a different fashion. Remember that MobX State Tree will protect your model properties from changes that occur outside actions, meaning that `model.property = null` won't work and MobX State Tree will throw an error to you. Using the `async/await` function expression with MobX State Tree won't work because of how the `async/await` works with `proxies` and the MobX State Tree protection, neither will the `Promises` approach; but fear not, there's still hope. `Generators` will work but in a different fashion.

MobX State Tree uses a "custom" approach to generators to deal with asynchronous actions so you can "await" for an asynchronous task to be completed. They have created a function called `flow` that takes in a generator as its main and only argument and will allow you to `yield` the function execution the same way that `async/await` does.

Let's take a look at an example:

```js { actualFilename=src/async.js endChar=1104 endLine=48 startChar=0 startLine=1 statedFilename=src/async.js url=https&#x3A;//gitlab.com/fullstackio/books/newline-guide-to-building-a-react-app-with-mobx-state-tree/module_01/lesson_01.08/src/async.js }
import { types, flow } from "mobx-state-tree";

const User = types
  .model("User", {
    id: types.identifier,
    name: types.string,
    lastName: types.string,
    age: types.number,
  })
  .views((self) => ({
    get fullName() {
      return `${self.name} ${self.lastName}`;
    },
  }))
  .actions((self) => ({
    updateName(name) {
      self.name = name;
    },
    updateLastName(name) {
      self.lastName = name;
    },
    updateAge(age) {
      self.age = age;
    },
  }));

const RootStore = types
  .model("RootStore", {
    users: types.array(User),
    selectedUser: types.safeReference(User),
    state: types.enumeration("idle", "fetching", "done", "error"),
  })
  .actions((self) => ({
    fetchUsers: flow(function* () {
      self.state = "fetching";
      try {
        const data = yield fetchUsersFromBackend();
        const users = yield data.json();
        self.users = users;
        self.state = "done";
      } catch (error) {
        console.error("Failed to fetch users", error);
        self.state = "error";
      }
      return self.users.length;
    }),
  }));
```

The `flow` function takes a `generator` (pay attention to the `*` at the function declaration) as the main and only argument and lets you `await` asynchronous actions with the reserved keyword, `yield`, which behaves exactly like `await`. Plain generators are more complex to handle on their own but MobX State Tree leverages this for you so you don't have to worry about it and deal with the `next()`, `return()`, and `throw()` behaviors that generators use.
