JAVASCRIPT
usereducer react
import React, { useReducer } from 'react'
import { render } from 'react-dom'
const types = {
PET: 'PET',
COLOR: 'COLOR',
}
const reducer = (state, action) => {
switch (action.type) {
case types.PET:
return { ...state, pet: action.value }
case types.COLOR:
return { ...state, color: action.value }
}
}
const initialState = {
color: 'black',
pet: 'cat',
}
export default function App() {
const [state, dispatch] = useReducer(reducer, initialState)
return (
<div>
<label>Choose a color and a pet: </label>
<br />
<select
value={state.color}
onChange={event => {
dispatch({ type: types.COLOR, value: event.target.value })
}}
>
<option value="black">Black</option>
<option value="pink">Pink</option>
<option value="blue">Blue</option>
</select>
<select
value={state.pet}
onChange={event => {
dispatch({ type: types.PET, value: event.target.value })
}}
>
<option value="cat">Cat</option>
<option value="dog">Dog</option>
<option value="mouse">Mouse</option>
</select>
<br />
<br />
You chose a {state.color} {state.pet}
</div>
)
}
render(<App />, document.querySelector('#app'))
useReducer
const initialState = {count: 0};
function reducer(state, action) {
switch (action.type) {
case 'increment':
return {count: state.count + 1};
case 'decrement':
return {count: state.count - 1};
default:
throw new Error();
}
}
function Counter() {
const [state, dispatch] = useReducer(reducer, initialState);
return (
<>
Count: {state.count}
<button onClick={() => dispatch({type: 'decrement'})}>-</button>
<button onClick={() => dispatch({type: 'increment'})}>+</button>
</>
);
}
useReducer
import './App.css';
import { useState, useReducer } from 'react';
function reducer(state, action) {
switch (action.type) {
case 'increment':
return ({ ...state, count: state.count + 1 })
case 'decrement':
return ({ ...state, count: state.count - 1 })
case 'tgColor':
return ({ ...state, color: (!state.color) })
case 'handleInputChange':
return ({ ...state, name: action.payload })
}
}
function App() {
const [state, dispatch] = useReducer(reducer, { count: 0, color: false, name: "" })
// const [name, setName] = useState("")
// const [count, setCount] = useState(0)
// const [color, setColor] = useState(false);
const handleInputChange = (e) => {
dispatch({ type: "handleInputChange", payload: e.target.value })
}
const colorCode = "#b81f00";
return (
<div className="App">
<form action="">
<input type="text" onChange={handleInputChange} value={state.name} placeholder="Enter Name" />
</form>
<h3 style={state.color ? { color: "red" } : { color: "black" }}>{state.count}</h3>
<button className="btn" onClick={() => dispatch({ type: "increment" })}>+</button>
<button className="btn" onClick={() => dispatch({ type: "decrement" })}>-</button>
<button className="btn" onClick={() => dispatch({ type: "tgColor" })}>Color</button>
<h2 style={state.color ? { color: "red" } : { color: "black" }}>{state.name}</h2>
</div>
);
}
export default App;
useReducer React
import React, { useReducer } from "react";
const reducer = (state, action) => {
switch (action.type) {
case "increment":
return { count: state.count + 1 };
break;
case "decrement":
return { count: state.count - 1 };
break;
default:
throw new Error();
}
};
const UseReduceExample = () => {
const [state, dispatch] = useReducer(reducer, initialCount );
return (
<>
Count: {state.count}
<button onClick={() => dispatch({ type: "increment" })}>+</button>
</>
);
};
export default UseReduceExample;
usereducer
import React from "react";
import { useReducer } from "react";
const initialState = {
count: 0,
};
type ReducerProps = {
state: any;
};
const reducer = (state: state, action) => {
switch (action.type) {
case "increment":
return { count: state.count + action.payload };
case "decrement":
return { count: state.count - action.payload };
default:
return state;
}
};
const Counter = () => {
const [state, dispatch] = useReducer(reducer, initialState);
return (
<div>
Count : {state.count}
<button
onClick={() => {
dispatch({ type: "increment", payload: 1 });
}}
>
Increment ++
</button>
<button
onClick={() => {
dispatch({ type: "decrement", payload: 1 });
}}
>
Decrement --
</button>
</div>
);
};
export default Counter;
useReducer React
import React, { useReducer } from "react";
const reducer = (state, action) => {
switch (action.type) {
case "increment":
return { count: state.count + 1 };
break;
case "decrement":
return { count: state.count - 1 };
break;
default:
throw new Error();
}
};
const UseReduceExample = () => {
const [state, dispatch] = useReducer(reducer, initialCount );
return (
<>
Count: {state.count}
<button onClick={() => dispatch({ type: "increment" })}>+</button>
</>
);
};
export default UseReduceExample;
useReducer React
import React, { useReducer } from "react";
const reducer = (state, action) => {
switch (action.type) {
case "increment":
return { count: state.count + 1 };
break;
case "decrement":
return { count: state.count - 1 };
break;
default:
throw new Error();
}
};
const UseReduceExample = () => {
const [state, dispatch] = useReducer(reducer, initialCount );
return (
<>
Count: {state.count}
<button onClick={() => dispatch({ type: "increment" })}>+</button>
</>
);
};
export default UseReduceExample;
useReducer React
import React, { useReducer } from "react";
const reducer = (state, action) => {
switch (action.type) {
case "increment":
return { count: state.count + 1 };
break;
case "decrement":
return { count: state.count - 1 };
break;
default:
throw new Error();
}
};
const UseReduceExample = () => {
const [state, dispatch] = useReducer(reducer, initialCount );
return (
<>
Count: {state.count}
<button onClick={() => dispatch({ type: "increment" })}>+</button>
</>
);
};
export default UseReduceExample;
useReducer React
import React, { useReducer } from "react";
const reducer = (state, action) => {
switch (action.type) {
case "increment":
return { count: state.count + 1 };
break;
case "decrement":
return { count: state.count - 1 };
break;
default:
throw new Error();
}
};
const UseReduceExample = () => {
const [state, dispatch] = useReducer(reducer, initialCount );
return (
<>
Count: {state.count}
<button onClick={() => dispatch({ type: "increment" })}>+</button>
</>
);
};
export default UseReduceExample;
useReducer React
import React, { useReducer } from "react";
const reducer = (state, action) => {
switch (action.type) {
case "increment":
return { count: state.count + 1 };
break;
case "decrement":
return { count: state.count - 1 };
break;
default:
throw new Error();
}
};
const UseReduceExample = () => {
const [state, dispatch] = useReducer(reducer, initialCount );
return (
<>
Count: {state.count}
<button onClick={() => dispatch({ type: "increment" })}>+</button>
</>
);
};
export default UseReduceExample;
useReducer React
import React, { useReducer } from "react";
const reducer = (state, action) => {
switch (action.type) {
case "increment":
return { count: state.count + 1 };
break;
case "decrement":
return { count: state.count - 1 };
break;
default:
throw new Error();
}
};
const UseReduceExample = () => {
const [state, dispatch] = useReducer(reducer, initialCount );
return (
<>
Count: {state.count}
<button onClick={() => dispatch({ type: "increment" })}>+</button>
</>
);
};
export default UseReduceExample;
useReducer React
import React, { useReducer } from "react";
const reducer = (state, action) => {
switch (action.type) {
case "increment":
return { count: state.count + 1 };
break;
case "decrement":
return { count: state.count - 1 };
break;
default:
throw new Error();
}
};
const UseReduceExample = () => {
const [state, dispatch] = useReducer(reducer, initialCount );
return (
<>
Count: {state.count}
<button onClick={() => dispatch({ type: "increment" })}>+</button>
</>
);
};
export default UseReduceExample;
useReducer
function init(initialCount) { return {count: initialCount};}
function reducer(state, action) {
switch (action.type) {
case 'increment':
return {count: state.count + 1};
case 'decrement':
return {count: state.count - 1};
case 'reset': return init(action.payload); default:
throw new Error();
}
}
function Counter({initialCount}) {
const [state, dispatch] = useReducer(reducer, initialCount, init); return (
<>
Count: {state.count}
<button
onClick={() => dispatch({type: 'reset', payload: initialCount})}> Reset
</button>
<button onClick={() => dispatch({type: 'decrement'})}>-</button>
<button onClick={() => dispatch({type: 'increment'})}>+</button>
</>
);
}
useReducer() hook react
code snippet
https://codesandbox.io/s/usereducer-demo-zxguu?file=/src/App.js
usereducer
const [state, dispatch] = useReducer(
reducer,
{count: initialCount} );
usereducer react
const [state, dispatch] = useReducer(reducer, initialArg, init);
what does the useReducer do in react
const [state, dispatch] = useReducer(reducer, initialState);
useReducer in react
const [state, dispatch] = useReducer(
reducer,
{count: initialCount}
);
useReducer in react
function init(initialCount) {
return {count: initialCount};
}
function reducer(state, action) {
switch (action.type) {
case 'increment':
return {count: state.count + 1};
case 'decrement':
return {count: state.count - 1};
case 'reset':
return init(action.payload);
default:
throw new Error();
}
}
function Counter({initialCount}) {
const [state, dispatch] = useReducer(reducer, initialCount, init);
return (
<>
Count: {state.count}
<button
onClick={() => dispatch({type: 'reset', payload: initialCount})}>
Reset
</button>
<button onClick={() => dispatch({type: 'decrement'})}>-</button>
<button onClick={() => dispatch({type: 'increment'})}>+</button>
</>
);
}
useReducer
function reducer(state, action) {
switch (action.type) {
case 'incremented_age': {
// ✅ Instead, return a new object
return {
...state,
age: state.age + 1
};
}