Solution for the quiz posted on CodePen.

HTML:

    
Enter a list of numbers to calculate some statistics.

    

    

      

        Count:
        
      

      

        Sum:
        
      

      

        Average:
        
      

      

        Minimum:
        
      

      

        Maximum:

JavaScript:

  // How do you get the list of numbers from the input box?
  function getNumbers(inputId) {
    var input = document.getElementById(inputId);
    return input.value;
  }

  // How do you extract the numbers from
  // the list?
  function extractNumbersFromList(list) {
    if (list === "") {
      return [];
    }

    // Split the list into an array and use
    // the Array map() function to convert
    // each element in the array into a number.
    var listArray = list.split(",");
    return listArray.map(function (item) {
      return parseInt(item);
    });
  }

  // How can you calculate the statistics?
  function calculateStatistics(numbers) {
    var stats = {
      sum: 0,
      minimum: numbers[0],
      maximum: numbers[0]
    };
    for (var index = 0; index < numbers.length; ++index) {
      stats.sum += numbers[index];
      stats.maximum = Math.max(stats.maximum, numbers[index]);
      stats.minimum = Math.min(stats.minimum, numbers[index]);
    }

    stats.count = numbers.length;
      stats.average = stats.sum / stats.count;

    return stats;
  }

  // How do you put the results into the table?
  function updateCell(id, value) {
    var cell = document.getElementById(id);
    cell.innerHTML = value;
  }

  function updateCells(stats) {
    for (var property in stats) {
      updateCell(property, stats[property]);
    }
  }

  // When do you perform these actions?
  // (You need something to act as a
  // trigger.)
  var numberInput = document.getElementById("number-list");
  numberInput.oninput = function(event) {
    var list = getNumbers(event.target.id);
    var numbers = extractNumbersFromList(list);
    var stats = calculateStatistics(numbers);
    updateCells(stats);
  };