JSTask2.js

/**
 * This code uses the principle of single return per function.
 * I did not reassign any object. 
 * This enables a cleaner experience and a testable code.
 * 
 * Also note that I did not use "let" or "var (which is forbidden)".
 * I only used const, to prevent reassignment errors.
 */

const data = [
  { principal: 2500, time: 1.8 },
  { principal: 1000, time: 5 },
  { principal: 3000, time: 1 },
  { principal: 2000, time: 3 },
]

const rateFinder = (interestObject) => {
  const { principal, time } = interestObject;
  if (principal >= 2500 && time > 1 && time < 3) {
    return 3;
  } else if (principal >= 2500 && time >= 3) {
    return 4;
  } else if (principal < 2500 && time <= 1) {
    return 2;
  } else {
    return 1;
  }
}

const singleInterestCalc = (interestObject) => {
  const { principal, time } = interestObject;
  const rate = rateFinder(interestObject);

  const interest = (principal * rate * time) / 100;
  return interest;
}

const interestCalculator = (data) => {
  const interestData = data.map(i => singleInterestCalc(i));
  console.log(interestData);
  return interestData;
}

interestCalculator(data);