Code examples for mrbalihai.github.io/2016/02/07/javascript-function-composition.html

es5-example.js

var add = function(a, b) { return a + b; };
var sum = function (arr) { return arr.reduce(add, 0) };
var getProperty = function(obj, propName) { return obj[propName]; };

var getWhisky = function (obj) { return getProperty(obj, 'whisky' };
var getPrices = function (arr) {
  return arr.map(function (a) {
    return getProperty(a, 'price');
  });
};

var getTotalWhiskyPrice = function (obj) {
  return sum(getPrices(getWhisky(obj)));
};

getTotalWhiskyPrice(products); // => 176.4

es6-example.js

let add = (a, b) => a + b;
let sum = (arr) => arr.reduce(add, 0);
let getProperty = (obj, propName) => obj[propName];

let getWhisky = (obj) => getProperty(obj, 'whisky');
let getPrices = (arr) => arr.map((a) => getProperty(a, 'price'));

let getTotalWhiskyPrice = (obj) => sum(getPrices(getWhisky(obj));

getTotalWhiskyPrice(products); // => 176.4

example-data.js

  var products = {
    'whisky': [
      {
        'name': 'Ardberg Uigeadail',
        'price': 54.35,
        'currency': 'GBP'
      },
      {
        'name': 'Laphroaig Quarter Cask',
        'price': 39.95,
        'currency': 'GBP'
      },
      {
        'name': 'Klichoman Machir Bay',
        'price': 42.25,
        'currency': 'GBP'
      },
      {
        'name': 'Talisker Storm',
        'price': 39.85,
        'currency': 'GBP'
      }
    ]
  };

lodash-pre-v4.js

var _ = require('lodash');

var getWhisky = _.partialRight(_.get, 'whisky');
var getPrices = _.partialRight(_.map, 'price');

var getTotalWhiskyPrice = _.flowRight(_.sum,
                                       getPrices,
                                       getWhisky);

getTotalWhiskyPrice(products); // => 176.4

ramda-lodash-fp.js

var _ = require('ramda'); 
// var _ = require('lodash/fp');

var getWhisky = _.prop('whisky');
var getPrices = _.map(_.prop('price')); // Using Ramda
//var getPrices = _.map('price'); // Using lodash-fp

var getTotalwhiskyPrice = _.compose(_.sum,
                                     getPrices,
                                     getWhisky);

getTotalWhiskyPrice(products); // => 176.4