Write code for humans!

Humans prefer this

Functional programming

          const kmOfItalianDrivers = users
  .filter(u => u.country === 'ITALY' && 
               u.hasDriverLicence &&
               u.age >= 18
  )
  .flatMap(u => u.cars)
  .reduce((totalKm, car) => totalKm + car.km, 0);
          

Machines prefer this

Imperative code

            let kmOfItalianDrivers = 0;

for (let i = 0; i < users.length; i++) {
  if (users[i].country === 'ITALY' &&
      users[i].hasDriverLicence &&
      users[i].age >= 18) {
        for (let j = 0; j < users[i].cars.length; j++) {
          kmOfItalianDrivers += users[i].cars[j].km;
        }
  }
}

return kmOfItalianDrivers;
            

Why humans prefer
functional programming

• It focuses on what you want to achieve
• Fewer lines of code
• It encourages code reusability (composing map, flatMap, filter, reduce etc.)
• It hides implementation details

Why machines prefer
imperative programming

• It focuses on how you want to achieve it
• You write what the machine should do
• Better performance (not always)