Reducer react

Reducer in react example

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>
    </>
  );
}

Source: reactjs.org

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>
    </>
  );
}

Source: reactjs.org

Reducer react

const getTotalItems = (items: CartItemType[]) =>
    items.reduce((ack: number, item) => ack + item.amount, 0);

Similar codes

105 votes286 views1 answer
Create react app scaffolding
Javascript React
9 votes227 views2 answers
Android center text react native
Javascript React
2 votes208 views2 answers
Easiest way to show current date in react
Javascript React
0 vote210 views1 answer
React link onclick refresh page
Javascript React
0 vote219 views1 answer
React-native-ffmpeg gradel issue
Javascript React
0 vote231 views1 answer
How to calc() height in react native for styling
Javascript React
1 vote236 views2 answers
React beforeunload
Javascript React
0 vote202 views1 answer
Horizontal scrollview in react js
Javascript React
0 vote246 views1 answer
React native map not loading
Javascript React
2 votes243 views1 answer
React native text right align
Javascript React