Todolist Example

Create Todolist project

We will create a simple todolist app where the user enters tasks and all tasks are listed in a table.

Create a new React App using Vite (Select React and JavaScript).
Create a new file called TodoList.jsx inside the src folder. Add the following code into the file.

TodoList.jsx
function TodoList() {
  return(
    <></>
  );
}

export default TodoList;

The todo item has one description field called desc.
We need one state for the description and one array state for all todos. Let’s declare states using the useState hook function.

TodoList.jsx
// Import useState from react
import { useState } from "react";

// Declare states
const [desc, setDesc] = useState("");
const [todos, setTodos] = useState([]);

The input element is used to collect data from a user
The addTodo function is invoked when the button is pressed

TodoList.jsx
  return(
    <>
      <input placeholder="Description" onChange={handleChange} value={desc} />
      <button onClick={addTodo}>Add</button>    
    </>
  );

The addTodo function adds a new todo item to the todos array state. We use spread notation (…) to add a new item at the end of the existing array.
The handleChange function store entered data to the desc state.

TodoList.jsx
const handleChange = (event) => {
  setDesc(event.target.value);
};

// Remember to call preventDefault() if using form
const addTodo = () => {
  setTodos([...todos, desc]);
};

Display todos

Next, we add the table element to the return statement and display all todos inside the table using the map() function.

TodoList.jsx
return (
  <>
    <input placeholder="Description" onChange={handleChange} value={desc} />
    <button onClick={addTodo}>Add</button>
    <table>
      <tbody>
        {todos.map((todo, index) => (
          <tr key={index}>
            <td>{todo}</td>
          </tr>
        ))}
      </tbody>
    </table>
  </>
);

You also have to export the TodoList component.

export default TodoList;

Finally, we render the TodoList component inside the App component's return statement

App.jsx
import "./App.css";
import TodoList from "./TodoList";

function App() {
  return (
    <>
      <TodoList />
    </>
  );
}

export default App;

Now, you can run the project using the following npm command:

npm run dev

Type some todos and see that they are displayed in the table.

Styling

Styles are defined in the App.css and index.css files. These are Vite's default styles, and you can use your own instead.
For example, the button style can be found in the index.css file

button {
  border-radius: 8px;
  border: 1px solid transparent;
  padding: 0.6em 1.2em;
  font-size: 1em;
  font-weight: 500;
  font-family: inherit;
  background-color: #1a1a1a;
  cursor: pointer;
  transition: border-color 0.25s;
}

The todolist is currently centered on the screen due to the body style setting place-items: center;. To move the todolist to the top of the screen, change this value to flex-start in the index.css file.

Now, your todolist should look the following:

TASKS

Try to implement the following features to your Todolist app.

Clear the input element after the Add button is pressed.
Add validation that an alert is shown if the desc state value is empty when new todo is added..

You can also add some styling to your table. For example, add the following styling to the App.css file:

table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 10px;
}

table th,
table td {
  border: 1px solid black;
  padding: 6px; 
}

Split components

Let's refactor the todolist example application by breaking it into multiple components. We'll use the todo item from the assignment, which also includes a due date.
We will add a new stateless component called TodoTable and separate it from the TodoList component.
Add a new file called TodoTable.jsx into the src folder. The starter code of the component is shown below.

import React from "react";

function TodoTable(props) {
  return <></>;
}

export default TodoTable;

note

The TodoTable component will be a stateless component. The stateless components are easy to test because they are pure functions. They are also simple to understand because they are just functions that takes props as input and returns JSX.

Finally, import the TodoTable component into TodoList component.

TodoList.jsx
import TodoTable from "./TodoTable";

Remove the HTML table element from the TodoList component's return statement and add the TodoTable component there.

TodoList.jsx
return (
  <>
    <input type="text" onChange={handleChange} value={desc} />
    <button onClick={addTodo}>Add</button>
    <TodoTable />
  </>
);

In this phase, our React app's component tree is the following:

React dataflow is one-way from top to bottom in the component tree.
The TodoTable component will be a child component of the TodoList component. Therefore, we can send data from the TodoList to TodoTable component by using the props.
Now, we can pass the todos state to the TodoTable component using props.

TodoList.jsx
<TodoTable todos={todos} />

Finally, we use map to render todos in the TodoTable component.

TodoTable.jsx
return (
  <table>
    <tbody>
      <tr>
        <th>Description</th>
        <th>Date</th>
      </tr>
      {props.todos.map((item, index) => (
        <tr key={index}>
          <td>{item.description}</td>
          <td>{item.date}</td>
        </tr>
      ))}
    </tbody>
  </table>
);

Vite and ESLint

Linters in programming are tools designed to analyze source code and identify potential issues, coding style violations, and error
ESLint is popular linter for JavaScript and TypeScript. Vite is using ESLint by default.
You can find the ESLint configuration file eslint.config.cjs from the root folder of your Vite project. You can define ESLint rules in this file to specify coding standards and guidelines for your project.
You might have seen that ESLint is giving a warning about missing PropTypes. We introduced PropTypes at the beginning of the course, but we haven't used them. React recommends using TypeScript instead of checking prop types at runtime.
You can exclude the PropTypes check by adding the highlighted line in your .eslint.config.cjs file:

eslint.config.cjs
export default [
  { ignores: ['dist'] },
  {
    files: ['**/*.{js,jsx}'],
    languageOptions: {
      ecmaVersion: 2020,
      globals: globals.browser,
      parserOptions: {
        ecmaVersion: 'latest',
        ecmaFeatures: { jsx: true },
        sourceType: 'module',
      },
    },
    settings: { react: { version: '18.3' } },
    plugins: {
      react,
      'react-hooks': reactHooks,
      'react-refresh': reactRefresh,
    },
    rules: {
      ...js.configs.recommended.rules,
      ...react.configs.recommended.rules,
      ...react.configs['jsx-runtime'].rules,
      ...reactHooks.configs.recommended.rules,
      'react/jsx-no-target-blank': 'off',
      'react-refresh/only-export-components': [
        'warn',
        { allowConstantExport: true },
      ],
      'react/prop-types': 0 
    },
  },
]

Create Todolist project​

Display todos​

Styling​

Split components​

Vite and ESLint​

Create Todolist project

Display todos

Styling

Split components

Vite and ESLint