How do i target React component which is clicked

Question

I want to change the class of a component when clicked.I use state to create a new component with the properties of name and done(which is upon creation false).Then this is pushed into the todos array. Now the question is how do I find which component is clicked and change its "done" property to?done ?

function App() {
    const [todos, setTodos] = useState([])
    const [newTodo, setNewTodo] = useState({
        name: "",
        done: false
    })

    const handleInput = (event) => {
        setNewTodo({name: event.target.value})
    }

    const handleDone = (event) => {

        //WHAT TO DO HERE

    }
    


    const submitTodo = (event) => {
        event.preventDefault();
        setTodos([...todos, newTodo.name])
        console.log(newTodo.name)
        setNewTodo({name: ""})
    }

  return (
    <div className="App">
        <form onSubmit={submitTodo}>
            <input onChange={handleInput} value={newTodo.name}/>
            <button>Add Todo!</button>
        </form>


        <ul>
            {todos.map(todo => (
                <li className={/*Change the class based on the DONE property*/} onClick={handleDone}>{todo}</li>
            ))}
        </ul>

    </div>
  );
}

export default App;

Answer 1

change your newTodo state

const [newTodo, setNewTodo] = useState('');
const [show,setShow] = useState(false);


const handleDone = (event) => setShow(!show)

.....
.....
.....

<li className={show ? 'classname when show is true': 'classname when show is false'} onClick={handleDone}>{todo}</li>

Answer 2

First of all, you should consistently make your todos contain both name and done properties. Having this you just pass the todo from the clicked <li> to your click handler so it can modify its done property and cause rerender by updating todos state.

function App() {
    const [todos, setTodos] = useState([])
    const [newTodo, setNewTodo] = useState({
        name: "",
        done: false
    })

    const handleInput = (event) => {
        setNewTodo({name: event.target.value, done: false }); // this now adds done property
    }

    const handleDone = (todo) => {
        todo.done = !todo.done;
        setTodos([...todos]); // This sets new todos to cause a rerender with updated list
    }
    
    const submitTodo = (event) => {
        event.preventDefault();
        setTodos([...todos, newTodo]) // this now appends entire newTodo item not only it's name
        setNewTodo({name: "", done: false}) // this now also sets default done
    }

  return (
    <div className="App">
        <form onSubmit={submitTodo}>
            <input onChange={handleInput} value={newTodo.name}/>
            <button>Add Todo!</button>
        </form>

        <ul>
            {todos.map(todo => (
                <li
                    className={todo.done ? 'classA' : 'classB'}
                    onClick={() => handleDone(todo)}
                >
                    {todo.name} // this now displays todo.name not todo
                </li>
            ))}
        </ul>

    </div>
  );
}

export default App;

Additionally you could extract todos and the click handler into a separate component:

function ToDo({ item }) {
   const [clicked, setClicked] = useState(item.done);

   const handleClick = useCallback(() => {
       item.done = !clicked
       setClicked(!clicked);
   }, [clicked]);

   return <li
       className={clicked ? 'classA' : 'classB'}
       onClick={handleClick}
   >
       {item.name}
    </li>;
}

Then just render a list of components with your App component:

<ul>
    {todos.map(todo => <ToDo item={todo} />
</ul>