Mini-Build: Student Grade Manager

Build a Student Grade Manager using objects, classes, methods, and array operations. This project combines all concepts from this module — object-oriented design with practical data management.

15 min•By Priygop Team•Updated 2026

Grade Manager Features

Student class — name, ID, grades array
Add grades — push grades to student's array
Calculate average — reduce to sum, divide by length
Get highest/lowest — Math.max/min with spread
Class ranking — sort students by average
JSON export — serialize data for storage

Student Manager Code

class Student {
  constructor(name, id) {
    this.name = name;
    this.id = id;
    this.grades = [];
  }

  addGrade(subject, score) {
    this.grades.push({ subject, score });
  }

  get average() {
    if (this.grades.length === 0) return 0;
    const sum = this.grades.reduce((acc, g) => acc + g.score, 0);
    return Math.round(sum / this.grades.length * 10) / 10;
  }

  get highest() {
    return Math.max(...this.grades.map(g => g.score));
  }

  get letterGrade() {
    const avg = this.average;
    if (avg >= 90) return "A";
    if (avg >= 80) return "B";
    if (avg >= 70) return "C";
    if (avg >= 60) return "D";
    return "F";
  }

  toString() {
    return `${this.name} (ID: ${this.id}) — Avg: ${this.average} (${this.letterGrade})`;
  }
}

// Create students
const students = [
  new Student("Alice", "S001"),
  new Student("Bob", "S002"),
  new Student("Charlie", "S003"),
];

// Add grades
students[0].addGrade("Math", 95);
students[0].addGrade("Science", 88);
students[0].addGrade("English", 92);

students[1].addGrade("Math", 78);
students[1].addGrade("Science", 82);
students[1].addGrade("English", 74);

students[2].addGrade("Math", 88);
students[2].addGrade("Science", 91);
students[2].addGrade("English", 85);

// Display all students
console.log("📊 Student Report:");
students.forEach(s => console.log(`  ${s.toString()}`));

// Ranking by average
const ranked = [...students].sort((a, b) => b.average - a.average);
console.log("\n🏆 Class Ranking:");
ranked.forEach((s, i) => console.log(`  #${i + 1}: ${s.name} — ${s.average}`));

// Export as JSON
console.log("\n📄 JSON Export:");
console.log(JSON.stringify(students, null, 2));

Tip

Make methods return 'this' to enable method chaining: student.addGrade('Math', 95).addGrade('Science', 88). This fluent API pattern is used in jQuery, D3.js, and many builder patterns.

Diagram

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keys/values/entries return arrays for .map/.filter.

Common Mistake

Warning

Using Math.max() on an empty array with spread returns -Infinity: Math.max(...[]) === -Infinity. Always check array length first or provide a fallback: grades.length > 0 ? Math.max(...grades) : 0.

Practice Task

Note

Extend the Grade Manager: (1) Add a getSubjectAverage(subject) method. (2) Add a static method to find the class topper. (3) Add a method that returns passing/failing status (average >= 60). (4) Export and re-import the data with JSON.

Quick Quiz

Key Takeaways

Build a Student Grade Manager using objects, classes, methods, and array operations.
Student class — name, ID, grades array
Add grades — push grades to student's array
Calculate average — reduce to sum, divide by length

Topics in This Module