JS Bin// source http://jsbin.com/cequnu

Redux 5:Writing a counter with redux final

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

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

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

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

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

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

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

console.log('Test passed!');

Redux:Writing a counter with redux step 1

'use strict';

function counter(state, action) {
  return state;
}

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

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

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

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

console.log('Test passed!');

Redux:Writing a counter with redux step 2

function counter(state, action) {
  if (action.type === 'INCREMENT') {
    return state + 1;
  } else if (action.type === 'DECREMENT') {
    return state - 1;
  }
}

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

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

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

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

console.log('Test passed!');

Redux:Writing a counter with redux step 3

function counter(state, action) {
  if (action.type === 'INCREMENT') {
    return state + 1;
  } else if (action.type === 'DECREMENT') {
    return state - 1;
  } else {
    return state;
  }
}

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

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

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

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

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

console.log('Test passed!');

Redux:Writing a counter with redux step 4

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

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

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

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

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

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

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

console.log('Test passed!');