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redux-legacyreducerintermediate

Array State — Adding Items

📖 Usage Example
function reducer(state = [], action) {
  switch (action.type) {
    case 'ADD_ITEM': return [...state, action.payload]
    default: return state
  }
}
reducer(['a'], { type: 'ADD_ITEM', payload: 'b' }) // → ['a', 'b']

Spread the existing array and append the new item to produce an immutable update.

Array State — Adding Items

When state is an array, never push directly (that would mutate state). Instead, use the spread operator to create a new array:

case 'ADD_ITEM': return [...state, action.payload]

This returns a brand-new array that includes all existing items plus the new one.

Challenge: Implement reducer(state = [], action) that handles 'ADD_ITEM' by returning a new array with the payload appended.

💡 Hints (2)
  • • `[...state, action.payload]` creates a new array without mutating the existing one.
  • • Avoid `state.push()` — it mutates state in place, which breaks Redux's change detection.