const mark = {
  firstName: "Mark",
  lastName: "Miller",
  fullName: `${this.firstName} ${this.lastName}`,
  mass: 78,
  height: 1.69,
  bmi: null,
  calcBMI: function () {
    this.bmi = this.mass / (this.height * this.height);
    return this.bmi;
  },
};

const john = {
  firstName: "John",
  lastName: "Smith",
  fullName: `${this.firstName} ${this.lastName}`,
  mass: 92,
  height: 1.95,
  bmi: null,
  calcBMI: function () {
    this.bmi = this.mass / (this.height * this.height);
    return this.bmi;
  },
};

const higherBMI = function () {
  john.calcBMI();
  mark.calcBMI();

  return john.BMI > mark.bmi
    ? `${john.firstName}'s BMI (${john.bmi}) is higher than ${mark.firstName}'s (${mark.bmi})! `
    : `${mark.firstName}'s BMI (${mark.bmi}) is higher than ${john.firstName}'s (${john.bmi})! `;
};

console.log(higherBMI());