Combine components, state, events and lists.
✍️ 3 exercises + code challenge in this lessonThis small app uses everything from the tutorial:
useState for the todo list and the inputonSubmitTry extending it: add an "edit" button, a filter (all / active / done), or save todos in localStorage with useEffect.
Mastering React Mini Project: Todo App helps you write clean and reliable React code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.
<div id="root"></div>
<script src="https://unpkg.com/react@18.3.1/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@18.3.1/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/@babel/standalone@7.25.6/babel.min.js"></script>
<script type="text/babel">
const { useState, useEffect, useRef, useMemo, createContext, useContext } = React;
function TodoItem({ todo, onToggle, onDelete }) {
return (
<li style={{ display: "flex", gap: 8, alignItems: "center", padding: "4px 0" }}>
<input type="checkbox" checked={todo.done} onChange={() => onToggle(todo.id)} />
<span style={{ flex: 1, textDecoration: todo.done ? "line-through" : "none" }}>{todo.text}</span>
<button onClick={() => onDelete(todo.id)}>✕</button>
</li>
);
}
function App() {
const [todos, setTodos] = useState([
{ id: 1, text: "Learn JSX", done: true },
{ id: 2, text: "Practise hooks", done: false },
]);
const [text, setText] = useState("");
const add = (e) => {
e.preventDefault();
if (!text.trim()) return;
setTodos([...todos, { id: Date.now(), text, done: false }]);
setText("");
};
const toggle = (id) => setTodos(todos.map(t => t.id === id ? { ...t, done: !t.done } : t));
const remove = (id) => setTodos(todos.filter(t => t.id !== id));
const left = todos.filter(t => !t.done).length;
return (
<div style={{ maxWidth: 360, fontFamily: "sans-serif" }}>
<h2>My Todos ({left} left)</h2>
<form onSubmit={add}>
<input value={text} onChange={e => setText(e.target.value)} placeholder="New todo" />
<button>Add</button>
</form>
<ul style={{ listStyle: "none", padding: 0 }}>
{todos.map(t => <TodoItem key={t.id} todo={t} onToggle={toggle} onDelete={remove} />)}
</ul>
</div>
);
}
ReactDOM.createRoot(document.getElementById("root")).render(<App />);
</script>Check what you learned in “React Mini Project: Todo App”.
Create a new array with the extra item instead of mutating the old one.
setTodos(todos.(newTodo));
How do you remove an item from a state array?
Render the todos as <li> elements and show "2 left" in a <p> (count todos where done is false).
Free sign-in required · Google login available
Stuck on something?
Ask the community in the CodesInTech forum.
Need a developer?
Learning on your own is great — and when you need professional help, our team builds custom software, websites and mobile apps for clients worldwide.
Explore Our Services