Ben Ben - 2 months ago 20
Javascript Question

react-redux update item in array doesn't re-render

I have a reducer which returns an object with an array in the object. I render the list of items in the array and when the user clicks on that item I want to re-render the array (or at least the item). I've created a jsbin that shows the problem:

https://jsbin.com/fadudeyaru/1/edit?js,console,output

To reproduce the issue, click the + or - button a few times to create a history. then click on one of the history items. you'll notice that the console log notices the event, and updates the state, but the list is not re-rendered. This can be verified by clicking the +/- button again after clicking on an item in the list. after that you'll see that it renders correctly.

Question is why does react-redux not cause this to be re-rendered? is there something I need to do to force the issue?

Thanks in advance.

Answer

State in redux is immutable. This means that reducer should create a new state for every mutation. Preferably, a deep clone should be done when arrays are present. The following code does an approximate deep clone for your code to work. Try utilities like lodash/deepClone for an easier solution.

const counter = (state = {count:0, history:[]}, action) => {
  let {count} = state;
  let history = [...state.history];

  switch (action.type) {
    case 'SELECT':
      history[action.i].selected = true;
      break;
    case 'INCREMENT':
      history.push({count,selected:false});
      count++;

      break;
    case 'DECREMENT':
      history.push({count,selected:false});
      count--;
      break;
    default:
      break;
  }
    console.log("count reducer: ", {count,history})
  return {count,history};
}