Redux : Reducer Function Example

reducer_example.js

// Reducer for counter. 
// Dependency : https://github.com/mjackson/expect

// handles default state
const counter = ( state = 0, action) => {
  switch( action.type ) {
    case 'INCREMENT':
      return state+1;
    case 'DECREMENT':
      return state-1;
    // handles undefined action
    default:
      return state;
  } 
}

expect(
  counter(0, { type: 'INCREMENT' })
).toEqual(1);

expect(
  counter(1, { type: 'INCREMENT' })
).toEqual(2);

expect(
  counter(1,{ type: 'SOMETHING_ELSE' })
).toEqual(1);

expect(
  counter(undefined, {})
).toEqual(0);

console.log("Test Passed");