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

# TodoItem

Based on several hooks we created, we can now create the TodoItem component.

```javascript
// ./components/TodoItem.js

import React from 'react';

import { useQuery } from '../hooks/useQuery';
import { useDeleteTodo } from '../hooks/useDeleteTodo';
import { useToggleTodo } from '../hooks/useToggleTodo';
import { useFlasher } from '../utils';

const renderHighlight = (title, query) => {
  if (!query) return title;
  const index = title.indexOf(query);
  if (index === -1) return title;
  return (
    <React.Fragment>
      {title.slice(0, index)}
      <b>{query}</b>
      {title.slice(index + query.length)}
    </React.Fragment>
  );
};

const TodoItem = ({ id, title, completed }) => {
  const { getQuery } = useQuery();
  const deleteTodo = useDeleteTodo();
  const toggleTodo = useToggleTodo();
  return (
    <li ref={useFlasher()}>
      <input
        type="checkbox"
        checked={!!completed}
        onChange={() => toggleTodo(id)}
      />
      <span
        style={{
          textDecoration: completed ? 'line-through' : 'none',
        }}
      >
        {completed ? title : renderHighlight(title, getQuery())}
      </span>
      <button onClick={() => deleteTodo(id)}>Delete</button>
    </li>
  );
};

export default React.memo(TodoItem);
```

We wrap this component with React.memo when exporting. This allows eliminating re-renders if this item is not changed.

# Next

In the next lesson, we create a component `NewTodo` to create a new ToDo item.

# TodoItem

Based on several hooks we created, we can now create the TodoItem component.

```javascript
// ./components/TodoItem.js

import React from 'react';

import { useQuery } from '../hooks/useQuery';
import { useDeleteTodo } from '../hooks/useDeleteTodo';
import { useToggleTodo } from '../hooks/useToggleTodo';
import { useFlasher } from '../utils';

const renderHighlight = (title, query) => {
  if (!query) return title;
  const index = title.indexOf(query);
  if (index === -1) return title;
  return (
    <React.Fragment>
      {title.slice(0, index)}
      <b>{query}</b>
      {title.slice(index + query.length)}
    </React.Fragment>
  );
};

const TodoItem = ({ id, title, completed }) => {
  const { getQuery } = useQuery();
  const deleteTodo = useDeleteTodo();
  const toggleTodo = useToggleTodo();
  return (
    <li ref={useFlasher()}>
      <input
        type="checkbox"
        checked={!!completed}
        onChange={() => toggleTodo(id)}
      />
      <span
                 textDecoration: completed ? 'line-through' : 'none',
        }}
      >
        {completed ? title : renderHighlight(title, getQuery())}
      </span>
      <button onClick={() => deleteTodo(id)}>Delete</button>
    </li>
  );
};

export default React.memo(TodoItem);
```

We wrap this component with React.memo when exporting. This allows eliminating re-renders if this item is not changed.

# Next

In the next lesson, we create a component `NewTodo` to create a new ToDo item.

In this lesson, we create a component to show one 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

TodoItem Component

TodoItem