test pipe

application.controller.js

import Ember from 'ember';

const { Controller } = Ember;

export default Controller.extend({
  init() {
    this._super(...arguments);
    this.cart = [
      { id: 0, name: 'Socks', price: 5 },
      { id: 1, name: 'Shoes', price: 50 }
    ];
      
    this.item = {
      id: 2,
      name: 'Dog Treats',
      price: 12
    }
  }
});

application.template.hbs

<h1>Warning: Contrived Example</h1>

Cart value: {{totalPrice}}

<ul>
	{{#each cart as |product|}}
    <li>{{product.name}} - $ {{product.price}}</li>
	{{/each}}
</ul>


<button {{action 
	(pipe 
  	(append cart) 
    (reduceBy "price") 
    (curry-concat "$") 
    (action (mut totalPrice))
  ) item}}>
  Add {{item.name}} - {{item.price}} to Cart
</button>

helpers.append.js

import Ember from 'ember';

export function append([b, a]/*, hash*/) {
  let arity = arguments[0].length;
  if (arity === 2) {
  	return [...a, ...b];
  }
  
  if (arity === 1) {
  	return function(curried) {
      b.pushObject(curried);
    	return b;
    }	
  }
}

export default Ember.Helper.helper(append);

helpers.curry-concat.js

import Ember from 'ember';

export function curryConcat([b, a]/*, hash*/) {
	let arity = arguments[0].length;
	
  if (arity === 2) {
  	return a.concat(b);
  }
  
  if (arity === 1) {
  	return function(curried) {
    	return b.concat(curried);
    };
  }
}

export default Ember.Helper.helper(curryConcat);

helpers.pipe.js

import Ember from 'ember';

const { Helper: { helper } } = Ember;

export function pipe(actions = []) {
  return function(...args) {
    return actions.reduce((acc, curr, idx) => {
      if (idx === 0) {
        return curr(...args);
      }
      return curr(acc);
    }, undefined);
  };
}

export default helper(pipe);

helpers.reduce-by.js

import Ember from 'ember';

const { get, isEmpty } = Ember;

function _reduce(key, array) {
	array = isEmpty(array) ? [] : array;
  return array.reduce((acc, item) => {
    return acc + get(item, key);
  }, 0);
}

export function reduceBy([reduceByKey, array]/*, hash*/) {
  let arity = arguments[0].length;
  
  if (arity === 2) {
    return _reduce(reduceByKey, array);
  }
  
  if (arity === 1) {
    return function(curried) {
  		return _reduce(reduceByKey, curried);
    }
  }
}

export default Ember.Helper.helper(reduceBy);

twiddle.json

{
  "version": "0.6.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.3.1/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.3.3/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember-template-compiler.js"
  }
}