Build a small JavaScript application that will increase or decreased a counter based on the action provided.

1. Create a new file named counter.js
2. Define action-types as constants:

      const INCREMENT_COUNTER = 'INCREMENT_COUNTER' 
      const DECREMENT_COUNTER = 'DECREMENT_COUNTER' 

3. Define two action creators for generating two kinds of actions to increment and decrement the counter:

      const increment = (by) => ({ 
          type: INCREMENT_COUNTER, 
          by, 
      }) 
      const decrement = (by) => ({ 
          type: DECREMENT_COUNTER, 
          by, 
      }) 

4. Initialize the initial accumulator to 0, then reduce it by passing several actions. The reducer function will decide which kind of action to perform based on the action type:

      const reduced = [ 
          increment(10), 
          decrement(5), 
          increment(3), 
      ].reduce((accumulator, action) => { 
          switch (action.type) { 
              case INCREMENT_COUNTER: 
            return accumulator + action.by 
              case DECREMENT_COUNTER: 
                  return accumulator - action.by 
              default: 
                  return accumulator 
          } 
      }, 0) 

5. Log the resulting value:

      console.log(reduced) 

6. Save the file
7. Open a terminal and run:

       node counter.js
  

7. Outputs: 8