Want more from your frontend framework!

Fulcr-x-Redux-talk.md

Source code for my Telia Full Stack Feast talk "Want more from your frontend framework!" (slides) (6/2020), comparing Redux with REST and a Fulcro with Pathom (Graph API).

Use case we are implementing: Show “hot deals” in your webshop, loaded on-demand.

PS: For the sake of simplicity I am cheating a little and presenting the Fulcro HotDeals component as a root component. If it was used as a child, we would need to either change the a Link Query or make sure that the :deals are presented as a property on the parent component. Also, I use unqualified keys for brevity. This is not recommended in practice.

traditional-redux+rest.jsx

/** Traditional Redux + REST implementation */
import React from 'react';
import Redux from 'react-redux';

// ################################################# FRONTEND
// FRONTEND 1 - UI: HotDeals.jsx
export default HotDeals = Redux.connect(
  (state) => _.pick(state, ["deals", "dealsError", "dealsLoading"]),
  { loadHotDeals } // defined below
)(function HotDeals({deals, dealsError, dealsLoading, loadHotDeals}){
  React.useEffect(() => loadHotDeals(), []) // on mount
  if (!deals || dealsLoading) return <p>Loading....</p>
  if (dealsError)             return <p>Something went wrong</p>
  return                      <ul>{deals.map(deal => <Deal {...deal}/>)}</ul>
})

// FRONTEND 2: actions.js
export function loadHotDeals() {
  return {
    type: "LOAD_HOT_DEALS",
    promise: fetchHotDeals()
  }
}

// FRONTEND 3: backend-client.js
export function fetchHotDeals() {
  return fetch('https://backend/hot-deals')
     .then(res => res.json())
}

// FRONTEND 4: reducer.js
//import { handle } from 'redux-pack'; // 1 Promise action -> 4 events
export function reducer(state = myInitialState, action) {
  const { type, payload } = action;
  switch (type) {
    case "LOAD_HOT_DEALS":
      // The UI expects deals, dealsLoading, dealsError:
      return handle(state, action, {
        start: prevState => ({
          ...prevState,
          dealsLoading: true, dealsError: null
        }),
        finish: prevState =>
          ({ ...prevState, dealsLoading: false }),
        failure: prevState =>
          ({ ...prevState, dealsError: payload }),
        success: prevState =>
          ({ ...prevState, deals: payload })
      });
    // ... repeat ∀ data sources ...
  }
}

// ################################################## BACKEND
// BACKEND - BUSINESS: webshop.js
async function hotDeals(env) { return ...; }

// BACKEND - PLUMBING: controller.js
router.get('/hot-deals', async(req, res) =>
   res.json(await webshop.hotDeals(req.env)));

x-innovative-fulcro+graphapi.clj

;; Implementation based on Fulcro and Graph API (via Pathom)
;; ################################################# FRONTEND
;; FRONTEND - all of it: deals.cljs
(def deal-factory (fcomp/factory Deal)) ;; Deal component not shown

;; Syntax: [1, 2, ...] = "array", {:key "value", ...} = map, (something ...) = invoke something (a function, ...)
(defsc HotDeals [this props]
  {:query [{:deals (fcomp/get-query Deal)} [ffetch/marker-table :deals-marker]]  ; (1) (**)
   :use-hooks? true}
  (hooks/use-effect (fn [] (ffetch/load!                                         ;     (**)
                             this :deals Deal                                    ; (2)
                             {:marker :deals-marker}))                           ;     (**)
                    [])
  ;; NOTE: We say we need :deals in the query (1), we get them from props (3), 
  ;;       we load! them from the server (2) - all 3 must match (and Fulcro checks it)
  (let [marker (get props [ffetch/marker-table :deals-marker])]
    (cond
      (ffetch/loading? marker) (p "Loading...")
      (ffetch/failed? marker)  (p "Something went wrong...")
      :else                    (ul (map deal-factory (get props :deals))))))     ; (3)
;; (**) - highlights: 1) declarative data needs; 2) built-in load!; 3) built-in loading/failed tracking

;; ################################################# BACKEND
;; BACKEND - BUSINESS: webshop.clj
(defn hot-deals [env] ...)

;; BACKEND - PLUMBING: graph-api.clj
(pc/defresolver hot-deals [env _]
  {::pc/input  #{}
   ::pc/output [{:deals [:deal/id :deal/title ...]}]}                            ; (4)
  {:deals (hot-deals env)})
;; NOTE: The output key :deals, (4) matches the key FE queries for

;; In config:
 ... (pc/connect-plugin {::pc/register [hot-deals ...]}) ...