Employee Average Salaries | Victor Savkin's Functional TypeScript

employee_salaries.ts

// https://vsavkin.com/functional-typescript-316f0e003dc6

class Employee {
  constructor(public name: string, public salary: number) {}
}

class Department {
  constructor(public employees: Employee[]) {}

  works(employee: Employee): boolean {
    return this.employees.indexOf(employee) > -1;
  }
}

type Predicate<T> = (value: T) => boolean;

function and<T>(predicates: Predicate<T>[]): Predicate<T> {
  return (value) => predicates.every(p => p(value));
}

function filteredSalaries(employees: Employee[], conditions: Predicate<Employee>[]): number[] {
  const filtered = employees.filter(and(conditions));
  return filtered.map(e => e.salary);
}

function average(nums: number[]): number {
  const total = nums.reduce((a,b) => a + b, 0);
  return total / nums.length;
}

function averageFilteredSalary(employees: Employee[], conditions: Predicate<Employee>[]): number {
  return average(filteredSalaries(employees, conditions));
}

const empls = [
  new Employee("Jim", 100),
  new Employee("John", 200),
  new Employee("Liz", 120),
  new Employee("Penny", 30)
];

const sales = new Department([empls[0], empls[1]]);

const conditions = [
  (employee) => employee.salary > 50, 
  (employee) => sales.works(employee)
];

const salesAverageSalaryOver50 = averageFilteredSalary(empls, conditions);
console.log('salesAverageSalaryOver50:', salesAverageSalaryOver50);