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Employee Average Salaries | Victor Savkin's Functional TypeScript
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// 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); |
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