React Native By Example

Building reducers

Let's look at how we would build reducers to handle creating a new task and saving it into our list of tasks.

Assuming we're working with the following state tree:

{ 
  tasks: [ 
    { 
      title: 'Buy Milk', 
      completed: false, 
      dueDate: undefined 
    }, 
    { 
      title: 'Walk Dog', 
      completed: true, 
      dueDate: undefined 
    } 
  ], 
} 

In the interest of writing a pure function, we want to make sure that we're not mutating the state and instead re-assigning our state to contain the updated changes.

In an impure function, we would simply do something like this:

Don't do this!

function addTask (state, action) { 
  switch(action.type) { 
    case 'ADD_TASK': 
      state.tasks.push({ 
        title: action.title, 
        completed: false 
      }); 
      return state; 
    default: 
      return state; 
  } 
}; 

What ...