Example of declarative style

declarativeExample.js

/**
    Decalartive style example of a program that will find the average grade for classes with 
    more than one student enrolled.
**/

let courses = [
    { name: 'functional fundamentals', enrolled: 2, grade: 100, students: 30 },
    { name: 'category theory', enrolled: 2, grade: 80, students: 25 },
    { name: 'basket weaving', enrolled: 1, grade: 89, students: 43 }
];

function average(numbers) {
  const total = numbers.reduce((a,b) => a + b, 0);
  return (numbers.length == 0) ? 0 : total / numbers.length;
}

function pluck (objects, key) {
  return objects.map(object => object[key]);
}

let overOneEnrolled = courses.filter(course => course.enrolled > 1);
let averageGrade = average(pluck(overOneEnrolled, 'grade'));

console.info('The average grade for courses with more than one person enrolled: ', averageGrade);