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

# TodoList

Here is the code for listing ToDo items.

```javascript
import React from 'react';
import { useDispatch, useTrackedState } from './store';

import TodoItem from './TodoItem';
import NewTodo from './NewTodo';

const TodoList = () => {
  const dispatch = useDispatch();
  const state = useTrackedState();
  const setQuery = event => {
    dispatch({ type: 'SET_QUERY', query: event.target.value });
  };
  return (
    <div>
      <ul>
        {state.todos.map(({ id, title, completed }) => (
          <TodoItem key={id} id={id} title={title} completed={completed} />
        ))}
        <NewTodo />
      </ul>
      <div>
        Highlight Query for incomplete items:
        <input value={state.query} onChange={setQuery} />
      </div>
    </div>
  );
};

export default TodoList;
```

The `useDispatch` returns a function `dispatch`. When we dispatch an action it will invoke the reducer.

The `useTrackedState` returns a global state.

Notice this signature is exactly the  same as the usage of `useReducer`.

```javascript
const [state, dispatch] = useReducer(...);
```

We have another hook in React Tracked that can be used like this.

```javascript
const [state, dispatch] = useTracked();
```

There are two components this imports from other files, `TodoItem` and `NewTodo` which we will cover later.

# Next

In the next lesson, we create a TodoItem component.


In this lesson, we develop a component to display the list of ToDo items.

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

TodoList Component

TodoList