We are going to start by defining the reducer for the filter value. Let's define the filter reducer now:

1. Create a new src/reducers.js file and import the generateID function from the src/api.js file:

import { generateID } from './api'

2. In the src/reducers.js file, define a new function, which is going to handle the FILTER_TODOS action, and set the value accordingly:

function filterReducer (state, action) {
    if (action.type === 'FILTER_TODOS') {
        return action.filter
    } else {
        return state
    }
}

Now, the filterReducer  function is defined, and we can handle the FILTER_TODOS action properly.