Moving from high churn to low churn, single responsibility, common closure-y code

bad.js

function calculatebonus( employee, currentsalary ) {
  var bonus = 0;
  switch( employee.ReviewResult ) {
    case "Good": 
      return 0.025 * currentsalary;
    case "Great": 
      return 0.04 * currentsalary
    case "InvestementBanker": 
      return 2 * currentsalary;
  }

  return 0;
}

better.js

function getBonusCalculator( employee ) {
  switch( employee.ReviewResult) {
    case "Good": 
      return new StandardBonusCalculator();
    case "Great": 
      return new ThrowEmSomeDoughBonusCalculator();
    case "InvestementBanker": 
      return new OpenTheVaultsBonusCalculator();
  }

  return new NoBonusCalculator();
}

function calculatebonus( employee, currentsalary ) {
  var calc = getBonusCalculator( employee );

  return calc.getbonus(currentsalary);
}

muchbetter.js

function GoodReviewAndThreeYearsTenureBonusCalculator() {
  function applies(employee) {
    return employee.ReviewStatus === "Good" && employee.Tenure > 3 
  }

  function getbonus(currentsalary) {
    return 0.025 * employee.Tenure * currentsalary;
  }

  return { applies: applies, getbonus: getbonus};
}
registerCalculator(new GoodReviewAndThreeYearsTenureBonusCalculator());

function StandardTenureBonusCalculator() {
  function applies(employee) {
    return employee.ReviewStatus === "Good" && employee.Tenure > 3 
  }

  function getbonus(currentsalary) {
    return 0.025 * employee.Tenure * currentsalary;
  }

  return { applies: applies, getbonus: getbonus};
}
registerCalculator(new StandardTenureBonusCalculator());

// ... others

function getBonusCalculator( employee) {
  for( i = 0; i < allcalculators.length; i++ ) {
    var calc = allcalculators[i];

    if( calc.applies(employee) ) {
      return calc;
    }
  }

}

function calculatebonus( employee, currentsalary ) {
  var calc = getBonusCalculator( employee );

  return calc.getbonus(currentsalary);
}