A reusable solution to the lycanthrope log task

LycanthropeLog.js

const journal = []


function requestEventData() {
  let day = prompt('what day is it?')
  let activities = prompt('what activities did you do today?')
  let didJacTurn = confirm('Did you turn today?')
  
  /** 
  * where activities variable above, is a string in this format: 'eat, sleep, pizza, sleep'
  * .split(..) breaks the string into an array where each element is the word before a comma: ['eat', ' sleep', ' pizza', ' sleep']
  * .map(..) iterates through the array and mutate each element.
  * .trim() on each element removes white spaces at the beginning and end of the element: ['eat', 'sleep', 'pizza', 'sleep']
  * new Set(..): creates a collections of unique values and returns a Set Object (with unique elements) Set: ['eat', 'sleep', 'pizza']
  * [...]: spread operator extracts the elements from the Set object and encloses them in an Array object instead.
  **/
  let eventData = {
    day,
    activities: [...new Set(activities.split(',').map(x => x.trim()))],
    didJacTurn
  }
  
  return eventData
}
/**
 * Recursive function to add new entry to journal
 */
function addEntryToJournal() {
  let endOfWeek = confirm('has the week ended?')

  if (endOfWeek) {
    determineCause(journal)
    return 
  }
  
  let eventJournal = requestEventData()
  // push the entry to the journal array
  journal.push(eventJournal)
  // recursively call this function again, so this process repeats (until the basecase: endOfWeek === true @line 9, is met)
  addEntryToJournal()
}

/**
 * Function to determine what activities 
 * causes jac to turn
 */
function determineCause(selectedJournal) {
  /** 
  * @line 54
  * check if there are any entries
  * journal.length returns the number of elements in the array (0 if empty)
  * since (0) is a falsy value, we can treat as boolean.
  */
  if (selectedJournal.length) {
    /*
    * @line 60: 
    * .filter(..) creates a new array with all elements that pass the test
    * the test here is [elements where the property "didJacTurn" equals true
    */
    let daysTurned = selectedJournal.filter(day => day.didJacTurn === true)
    let allActivitiesOndaysTurned = []
	
    /*
    * .forEach(..) iterates over all the days jac turned
    * each day is an object in this format { day: "Monday", activities: ['eat', 'sleep' ...], didJacTurn: true } 
    * .concat(..) merges two or more arrays and returns a new array
    * we assign the result to the "allActivitiesOndaysTurned" variable
    */
    daysTurned.forEach(day => {
      allActivitiesOndaysTurned = allActivitiesOndaysTurned.concat(day.activities)
    })
    
    // map.entries returns the key value pair of activities and their frequency
    const map = arr.reduce((acc, e) => acc.set(e, (acc.get(e) || 0) + 1), new Map());
	
    /* 
    * find which entry has a value equal to daysTurned.length
    * those activities are similar activities done in all days jac turned
    * and would most likely be the cause of jac's predicament.
    */
    console.log(map)
    /** 
    Map(6)
      [[Entries]]
      0: {"eat" => 1}
      1: {"sleep" => 1}
      2: {"pizza" => 2}
      3: {"buy bread" => 1}
      4: {"breakfast" => 1}
      5: {"lunch" => 1}
      size: 6
    **/
    
  } else {
    console.log('You made no logs this week')
  }
}

addEntryToJournal()