#Higher order functions A higher-order function is a function that does at least one of the following:

-Takes one or more functions as an input

-Outputs a function

All other functions are first-order functions.

Experiments with higher order functions (array methods)

Use this array for all our examples:

var animals = [
	{name: 'Milo', type: 'cat', eyes: 2},
	{name: 'Peluza', type: 'cat', eyes: 2},
	{name: 'Yummy', type: 'cat', eyes: 2},
	{name: 'Doggy', type: 'dog', eyes: 2},
	{name: 'Sammy', type: 'dog', eyes: 2}
];

##Map It iterates over an array and return a new array with the changes you do to it.

Using map method:

const getAnimals = animals.map(animal => `${animal.name} is a ${animal.type}`);

This returns:

[ 'Milo is a cat',
  'Peluza is a cat',
  'Yummy is a cat',
  'Doggy is a dog',
  'Sammy is a dog' ]

##ForEach It iterates over an array and does not return anything unless you do it manually.

Using the forEach method:

const getAnimals2 = animals.forEach((animal) => `${animal.name} is a ${animal.type}`);

This returns: undefined

On this case we will need to create a new array manually if we want to have the same result of the map method.

##Filter It iterates over an array and return a filtered results based on a conditional passed inside the function.

Using the filter method to get only dogs:

const dogs = animals.filter(animal => animal.type === 'dog');

This returns the following:

[ { name: 'Doggy', type: 'dog', eyes: 2 },
  { name: 'Sammy', type: 'dog', eyes: 2 } ]

##Find It iterates over an array and return only 1 element, the first that matches with your conditional.

Using the find method to get only one element:

const sammy = animals.find(animal => animal.name === 'Sammy');

This returns: { name: 'Sammy', type: 'dog', eyes: 2 }

##Some It iterates over an array and return true if one of the items matches with the condition passed.

Using the check if there are cats in our array:

const thereAreCats = animals.some(animal => animal.type === 'cat');

This returns: true

##Every It iterates over an array and return true if ALL of the items matches with the condition passed.

Using the check if all the animals are dogs:

const areAllDogs = animals.every(animal => animal.type === 'dog');

This returns: false

##Reduce It iterates over an array and reduce it, using an accumulator logic, which merge the items inside the array, returning a new merged element.

Fusion all the animal names:

const fusionedAnimals = animals.reduce((newName, animal) => newName+animal.name, '');

This returns: MiloPeluzaYummyDoggySammy

##Chaining methods We can use the previous methods together, chaining them one after the other.

Get all dogs and fusion their names

const getDogsAndFusionThem = animals.filter(animal => animal.type === 'dog')
		.reduce((newName, animal) => newName+animal.name, '');

This returns: DoggySammy

More info can be found in:
Catching up with JS higher order functions
Fun with higher order functions
Elquent Javascript - Higher Order functions

Authors

Jose Pablo Granados

• github/jpgcode
• twitter/jpgcode

License

Copyright (c) 2016 Jose Pablo Granados Released under the MIT license