School Register

function updateSchoolRegister(studentData) {
    let register = {};
    let pattern = /^Student name: (?<name>[A-Z][a-z]+), Grade: (?<grade>\d+), Graduated with an average score: (?<score>\d\.\d+)$/;

    for (let line of studentData) {
        let { name, grade, score } = line.match(pattern).groups;
        let student = { name, score };

        if (score < 3) continue;

        grade = Number(grade) + 1;

        if (!(grade in register)) {
            register[grade] = [];
        }

        register[grade].push(student);
    }

    let output = Object.entries(register)
        .sort(sortGrades)
        .map(formatOutput)
        .join('\n');


    function sortGrades([gradeA], [gradeB]) {
        return +gradeA - +gradeB;
    }

    function averageScore(sum, { score }) {
        return sum + Number(score);
    }

    function getStudents(list, { name }) {
        list.push(name);
        return list;
    }

    function formatOutput([grade, students]) {
        let studentsCount = students.length;
        let averageClassScore = students.reduce(averageScore, 0) / studentsCount;
        let studentInfo = students.reduce(getStudents, []).join(', ');

        let msg = `${grade} Grade\n`;
        msg += `List of students: ${studentInfo}\n`;
        msg += `Average annual grade from last year: ${averageClassScore.toFixed(2)}\n`;

        return msg;
    }

    return output.trim();
}