Using JS conditionals

check-grades.js

function ifGrade(marks) {
  if (marks > 100) return 'Cheating is bad!';
  else if (marks >= 90) return 'A+';
  else if (marks >= 80) return 'A';
  else if (marks >= 70) return 'B+';
  else if (marks >= 60) return 'B';
  else if (marks >= 50) return 'C';
  else if (marks >= 40) return 'D';
  else return 'F';
}

// console.log(ifGrade(75));
// "B+"

function whichGrade(marks) {
  switch (true) {
    case marks > 100: return 'Cheating is bad!';
    case marks >= 90: return 'A+';
    case marks >= 80: return 'A';
    case marks >= 70: return 'B+';
    case marks >= 60: return 'B';
    case marks >= 50: return 'C';
    case marks >= 40: return 'D';
    default: return 'F';
  }
}

// console.log(whichGrade(75));
// "B+"

print-grades.js

var report = [
  { name: 'John', marks: 80 }, 
  { name: 'Smith', marks: 90 }, 
  { name: 'Doe', marks: 20 }
];

function printGradeOf(name) {
  const found = report.find(function(student) { 
    return student.name === name; 
  });
  // Change the whichGrade to ifGrade, if you wanna use if/else instead.
  found ? console.log(found.name, whichGrade(found.marks)) : console.log('Did not find your kid', name);
}

function printGrades() {
  console.log('Number of Students: ', report.length);
  report.forEach(function(s) { 
    // Change the whichGrade to ifGrade, if you wanna use if/else instead.
    console.log(s.name, whichGrade(s.marks));
  });
}

replace-conditions.js

var grades = [
  { min: 101, grade: 'Cheating is bad!' }, 
  { min: 90, grade: 'A+' }, 
  { min: 80, grade: 'A' }, 
  { min: 70, grade: 'B+' }, 
  { min: 60, grade: 'B' }, 
  { min: 50, grade: 'C' }, 
  { min: 40, grade: 'D' }, 
  { min: 0, grade: 'F', default: true }
];

// find the martching grade for the marks or the default.
function findGradeFor(marks) {
  const found = grades.find(function(grade) { return grade.min <= marks || !!grade.default; });
  
  return found.grade;
}

// findGradeFor(101);
// Cheating is bad!

// findGradeFor(75);
// "B+"

student-report.js

function addMarks(name, marks) { 
  report.push({ name, marks }); 
}

// addMarks('Sarah', 65);