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C # tutorial
The useReducer Hook is similar to the useState Hook.It allows for custom state logic.If you find yourself keeping track of multiple pieces of state that rely on complex logic, useReducer may be useful
The useReducer Hook accepts two arguments.
useReducer(<reducer>, <initialState>)
The reducer
function contains your custom state logic and the initialState
can be a simple value but generally will contain an object.
The useReducer
Hook returns the current state
and a dispatch
method.
Here is an example of useReducer
in a counter app:
import { useReducer } from "react";
import ReactDOM from "react-dom/client";
const initialTodos = [
{
id: 1,
title: "Todo 1",
complete: false,
},
{
id: 2,
title: "Todo 2",
complete: false,
},
];
const reducer = (state, action) => {
switch (action.type) {
case "COMPLETE":
return state.map((todo) => {
if (todo.id === action.id) {
return { ...todo, complete: !todo.complete };
} else {
return todo;
}
});
default:
return state;
}
};
function Todos() {
const [todos, dispatch] = useReducer(reducer, initialTodos);
const handleComplete = (todo) => {
dispatch({ type: "COMPLETE", id: todo.id });
};
return (
<>
{todos.map((todo) => (
<div key={todo.id}>
<label>
<input
type="checkbox"
checked={todo.complete}
onChange={() => handleComplete(todo)}
/>
{todo.title}
</label>
</div>
))}
</>
);
}
const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<Todos />);
This is just the logic to keep track of the todo complete status.
All of the logic to add, delete, and complete a todo could be contained within a single
useReducer
Hook by adding more actions.