Discover how React Tracked optimizes render performance in web apps. Build a to-do app using two methods, and gain skills to create advanced applications efficiently.

React Tracked is a small library for global state with React Hooks and
React Context. It allows you to develop a small web app with global state
without a bigger library like Redux.

In this course, you will create a to-do app. But before diving into
creating an application, you’ll first learn how React Tracked can solve
common performance issues around render optimization. Once you learn how to
work with this library, you’ll then build a to-do app through two different
methods.

By the end of this course, you will be ready to build more advanced
applications without having to do unnecessary re-rendering. You’ll also
have a nice piece to showcase in your portfolio.

React Tracked: Creating Web Apps with Global State

# useToggleTodo

This hook is to toggle the `completed` flag of an item.

```javascript
// ./hooks/useToggleTodo.js

import { useCallback } from 'react';
import { useSetDraft } from '../store';

export const useToggleTodo = () => {
  const setDraft = useSetDraft();
  return useCallback(
    id => {
      setDraft(draft => {
        const todo = draft.todos.find(todo => todo.id === id);
        if (todo) todo.completed = !todo.completed;
      });
    },
    [setDraft],
  );
};
```

Initially `todo.completed` is `undefined`, but once it's toggled it will be `true`, and `false` / `true` thereafter.

This hook can also be implemented without mutations. The immutable version is the following:

```javascript
setDraft(draft => ({ ...draft, todos: draft.todos.map(todo => (todo.id === id ? { ...todo, completed: !todo.completed } : todo)) }));
```

This might be a bit tricky if you aren't used to immutable updates.

# Next

In the next lesson, we learn about another hook `useQuery`.

In this lesson, we create a hook to toggle a ToDo item.

Creating a Counter App only with React Context

Introducing React Tracked to the Counter App

Developing ToDo App with React Tracked and useReducer

Developing ToDo App with React Tracked, useState and Immer

Going Further

useToggleTodo Hook

useToggleTodo