Functional Programming

high-order-functions.js

// Notes from funfunfunction videos
/*
Functional programming
According to the video FP should improve your code, less time and more understandable, in javascript functions are values 
*/
// functions can be assigned to variables
var triple = function (x) {
  return x * 3;
}
var waffle  = triple;
waffle(2);

/*
What are high order functions , componsition. The fact that you can pass a function as a value allows you to compose functions
*/
// For example filter 
// list of animals 
var animals = [
  { name: 'Fluffykins', species: 'rabbit'},
  { name: 'Caro',       species: 'dog'},
  { name: 'Halmiton',   species: 'dog'},
  { name: 'Harold',     species: 'fish'},
  { name: 'Ursula',     species: 'cat'},
  { name: 'Jimmy',      species: 'fish'}
];
// normal approach
var dogs = [];
for (var i = 0; i < animals.length; i++) {\
  if (animals[i].species === 'dog' ) {
     dogs.push(animals[i]);
  }
}
                                          
// fp way
var dogs = animals.filter(function(animal) {
  return animal.species === 'dog'; // one line of logic 
});                       
                                          
// breaking down the logic 
var isDog = function(animal) {
  return animal.species === 'dog';
};
                                          
var isNotDog = function(animal) {
  return animal.species !== 'dog';
};
                                          
// composition 
var dogs = animals.filter(isDog);
var otherAnimals = animals.filter(isNotDog);