Wiley  Mayer

Wiley Mayer

1603447200

Create simple POS with React.js, Node.js, and MongoDB #17: Stat screen

Defenition:_ POS – “Point of Sale”. At the point of sale, the merchant calculates the amount owed by the customer, indicates that amount, may prepare an invoice for the customer (which may be a cash register printout), and indicates the options for the customer to make payment._

In the previous chapter, we implemented the order page in our POS project. We successfully displayed the products and calculate the total price along with a calculator to calculate the change to be returned. Finally, each order transaction was saved to the database. This was one of the complex parts of our tutorial that we successfully tackled.

Now, we are going to implement the final chapter for this tutorial series where we are implementing a graphical representation section on our dashboard screen. In the dashboard screen, we are going o display the statistics from the database using the react-chart.js library. The main aim here is to show you how to add graphs to represent visual data in the React app that already uses redux as functionality.

So, let us get started!

Prepare data from the backend

first, we create a new endpoint for send stat data create a new file name api_state.js inside this file we add a function for fetching data from the product table

const express = require( “express”);

const router = express.Router();

const product = require( “./models/product_schema”);

router.get( “/stat/current_inventory”, async ( req, res) = > {

try {

await product.find({}).exec( function ( err, data) {

if ( err) {

console.log( err);

} else {

res.json({

result: “success”,

message: “Fetch product Successfully”,

data: data,

});

}

});

} catch ( err) {

res.json({ result: “error”, message: err. msg });

}

});

module. exports = router;

Next, we need to register the API endpoint to api.js using use middleware function provided by express library as shown in the code snippet below:

const express = require( “express”);

const router = express.Router();

require( “./db”);

router. use(require( “./api_stat”));

module. exports = router;

Thus, we are done on the backend. Now, we can move forward to implement our frontend which will include a chart diagram on the dashboard screen.

Installing Dependencies

In order to configure and display charts in our react app, we need to install some dependencies that we will make it possible. The required libraries are chart.js and react-chartjs-2 which we can install by running the following command in our project terminal:

1

yarn add react- chartjs-2 chart. js

Next, we need to import the chart components such as Bar, Doughnut, etc. to the dashboard.js file from react-chartjs-2 library as directed in the code snippet below:

1

import { Bar, Doughnut , Line } from “react-chartjs-2”;

Configuring Chart

Here, we are going to configure the chart by using the data that we are going to fetch from the API endpoint that we created earlier. We are going to use redux methodologies for getting the chart data as well. Hence, we need to create constant states first.

Defining Constants

Here, we are defining some constants for the configuring redux mechanism for the chart as shown in the code snippet below:

1

2

3

export const STAT_FETCHING = “STAT_FETCHING”;

export const STAT_SUCCESS = “STAT_SUCCESS”;

export const STAT_FAILED = “STAT_FAILED”;

Creating Reducer

Next, we need to create a reducer in order to access the Redux store. The code required to implement a reducer for the redux mechanism is provided in the code snippet below:

import { STAT_FETCHING, STAT_SUCCESS, STAT_FAILED } from “…/constants”;

const initialState = {

isFetching: false,

isError: false,

result: null,

};

export default ( state = initialState, { type, payload }) = > {

switch ( type) {

case STAT_FETCHING:

return { … state, isFetching: true, isError: false, result: null };

case STAT_FAILED:

return { … state, isFetching: false, isError: true, result: null };

case STAT_SUCCESS:

return { … state, isFetching: false, isError: false, result: payload };

default:

return state;

}

};

Creating Reducer

Next, we need to create a reducer in order to access the Redux store. The code required to implement a reducer for the redux mechanism is provided in the code snippet below:

JavaScript

import statReducer from “./stat.reducer”;

export default combineReducers({

statReducer,

});

#javascript #node.js #pos tutorial #react

What is GEEK

Buddha Community

Create simple POS with React.js, Node.js, and MongoDB #17: Stat screen
Autumn  Blick

Autumn Blick

1598839687

How native is React Native? | React Native vs Native App Development

If you are undertaking a mobile app development for your start-up or enterprise, you are likely wondering whether to use React Native. As a popular development framework, React Native helps you to develop near-native mobile apps. However, you are probably also wondering how close you can get to a native app by using React Native. How native is React Native?

In the article, we discuss the similarities between native mobile development and development using React Native. We also touch upon where they differ and how to bridge the gaps. Read on.

A brief introduction to React Native

Let’s briefly set the context first. We will briefly touch upon what React Native is and how it differs from earlier hybrid frameworks.

React Native is a popular JavaScript framework that Facebook has created. You can use this open-source framework to code natively rendering Android and iOS mobile apps. You can use it to develop web apps too.

Facebook has developed React Native based on React, its JavaScript library. The first release of React Native came in March 2015. At the time of writing this article, the latest stable release of React Native is 0.62.0, and it was released in March 2020.

Although relatively new, React Native has acquired a high degree of popularity. The “Stack Overflow Developer Survey 2019” report identifies it as the 8th most loved framework. Facebook, Walmart, and Bloomberg are some of the top companies that use React Native.

The popularity of React Native comes from its advantages. Some of its advantages are as follows:

  • Performance: It delivers optimal performance.
  • Cross-platform development: You can develop both Android and iOS apps with it. The reuse of code expedites development and reduces costs.
  • UI design: React Native enables you to design simple and responsive UI for your mobile app.
  • 3rd party plugins: This framework supports 3rd party plugins.
  • Developer community: A vibrant community of developers support React Native.

Why React Native is fundamentally different from earlier hybrid frameworks

Are you wondering whether React Native is just another of those hybrid frameworks like Ionic or Cordova? It’s not! React Native is fundamentally different from these earlier hybrid frameworks.

React Native is very close to native. Consider the following aspects as described on the React Native website:

  • Access to many native platforms features: The primitives of React Native render to native platform UI. This means that your React Native app will use many native platform APIs as native apps would do.
  • Near-native user experience: React Native provides several native components, and these are platform agnostic.
  • The ease of accessing native APIs: React Native uses a declarative UI paradigm. This enables React Native to interact easily with native platform APIs since React Native wraps existing native code.

Due to these factors, React Native offers many more advantages compared to those earlier hybrid frameworks. We now review them.

#android app #frontend #ios app #mobile app development #benefits of react native #is react native good for mobile app development #native vs #pros and cons of react native #react mobile development #react native development #react native experience #react native framework #react native ios vs android #react native pros and cons #react native vs android #react native vs native #react native vs native performance #react vs native #why react native #why use react native

NBB: Ad-hoc CLJS Scripting on Node.js

Nbb

Not babashka. Node.js babashka!?

Ad-hoc CLJS scripting on Node.js.

Status

Experimental. Please report issues here.

Goals and features

Nbb's main goal is to make it easy to get started with ad hoc CLJS scripting on Node.js.

Additional goals and features are:

  • Fast startup without relying on a custom version of Node.js.
  • Small artifact (current size is around 1.2MB).
  • First class macros.
  • Support building small TUI apps using Reagent.
  • Complement babashka with libraries from the Node.js ecosystem.

Requirements

Nbb requires Node.js v12 or newer.

How does this tool work?

CLJS code is evaluated through SCI, the same interpreter that powers babashka. Because SCI works with advanced compilation, the bundle size, especially when combined with other dependencies, is smaller than what you get with self-hosted CLJS. That makes startup faster. The trade-off is that execution is less performant and that only a subset of CLJS is available (e.g. no deftype, yet).

Usage

Install nbb from NPM:

$ npm install nbb -g

Omit -g for a local install.

Try out an expression:

$ nbb -e '(+ 1 2 3)'
6

And then install some other NPM libraries to use in the script. E.g.:

$ npm install csv-parse shelljs zx

Create a script which uses the NPM libraries:

(ns script
  (:require ["csv-parse/lib/sync$default" :as csv-parse]
            ["fs" :as fs]
            ["path" :as path]
            ["shelljs$default" :as sh]
            ["term-size$default" :as term-size]
            ["zx$default" :as zx]
            ["zx$fs" :as zxfs]
            [nbb.core :refer [*file*]]))

(prn (path/resolve "."))

(prn (term-size))

(println (count (str (fs/readFileSync *file*))))

(prn (sh/ls "."))

(prn (csv-parse "foo,bar"))

(prn (zxfs/existsSync *file*))

(zx/$ #js ["ls"])

Call the script:

$ nbb script.cljs
"/private/tmp/test-script"
#js {:columns 216, :rows 47}
510
#js ["node_modules" "package-lock.json" "package.json" "script.cljs"]
#js [#js ["foo" "bar"]]
true
$ ls
node_modules
package-lock.json
package.json
script.cljs

Macros

Nbb has first class support for macros: you can define them right inside your .cljs file, like you are used to from JVM Clojure. Consider the plet macro to make working with promises more palatable:

(defmacro plet
  [bindings & body]
  (let [binding-pairs (reverse (partition 2 bindings))
        body (cons 'do body)]
    (reduce (fn [body [sym expr]]
              (let [expr (list '.resolve 'js/Promise expr)]
                (list '.then expr (list 'clojure.core/fn (vector sym)
                                        body))))
            body
            binding-pairs)))

Using this macro we can look async code more like sync code. Consider this puppeteer example:

(-> (.launch puppeteer)
      (.then (fn [browser]
               (-> (.newPage browser)
                   (.then (fn [page]
                            (-> (.goto page "https://clojure.org")
                                (.then #(.screenshot page #js{:path "screenshot.png"}))
                                (.catch #(js/console.log %))
                                (.then #(.close browser)))))))))

Using plet this becomes:

(plet [browser (.launch puppeteer)
       page (.newPage browser)
       _ (.goto page "https://clojure.org")
       _ (-> (.screenshot page #js{:path "screenshot.png"})
             (.catch #(js/console.log %)))]
      (.close browser))

See the puppeteer example for the full code.

Since v0.0.36, nbb includes promesa which is a library to deal with promises. The above plet macro is similar to promesa.core/let.

Startup time

$ time nbb -e '(+ 1 2 3)'
6
nbb -e '(+ 1 2 3)'   0.17s  user 0.02s system 109% cpu 0.168 total

The baseline startup time for a script is about 170ms seconds on my laptop. When invoked via npx this adds another 300ms or so, so for faster startup, either use a globally installed nbb or use $(npm bin)/nbb script.cljs to bypass npx.

Dependencies

NPM dependencies

Nbb does not depend on any NPM dependencies. All NPM libraries loaded by a script are resolved relative to that script. When using the Reagent module, React is resolved in the same way as any other NPM library.

Classpath

To load .cljs files from local paths or dependencies, you can use the --classpath argument. The current dir is added to the classpath automatically. So if there is a file foo/bar.cljs relative to your current dir, then you can load it via (:require [foo.bar :as fb]). Note that nbb uses the same naming conventions for namespaces and directories as other Clojure tools: foo-bar in the namespace name becomes foo_bar in the directory name.

To load dependencies from the Clojure ecosystem, you can use the Clojure CLI or babashka to download them and produce a classpath:

$ classpath="$(clojure -A:nbb -Spath -Sdeps '{:aliases {:nbb {:replace-deps {com.github.seancorfield/honeysql {:git/tag "v2.0.0-rc5" :git/sha "01c3a55"}}}}}')"

and then feed it to the --classpath argument:

$ nbb --classpath "$classpath" -e "(require '[honey.sql :as sql]) (sql/format {:select :foo :from :bar :where [:= :baz 2]})"
["SELECT foo FROM bar WHERE baz = ?" 2]

Currently nbb only reads from directories, not jar files, so you are encouraged to use git libs. Support for .jar files will be added later.

Current file

The name of the file that is currently being executed is available via nbb.core/*file* or on the metadata of vars:

(ns foo
  (:require [nbb.core :refer [*file*]]))

(prn *file*) ;; "/private/tmp/foo.cljs"

(defn f [])
(prn (:file (meta #'f))) ;; "/private/tmp/foo.cljs"

Reagent

Nbb includes reagent.core which will be lazily loaded when required. You can use this together with ink to create a TUI application:

$ npm install ink

ink-demo.cljs:

(ns ink-demo
  (:require ["ink" :refer [render Text]]
            [reagent.core :as r]))

(defonce state (r/atom 0))

(doseq [n (range 1 11)]
  (js/setTimeout #(swap! state inc) (* n 500)))

(defn hello []
  [:> Text {:color "green"} "Hello, world! " @state])

(render (r/as-element [hello]))

Promesa

Working with callbacks and promises can become tedious. Since nbb v0.0.36 the promesa.core namespace is included with the let and do! macros. An example:

(ns prom
  (:require [promesa.core :as p]))

(defn sleep [ms]
  (js/Promise.
   (fn [resolve _]
     (js/setTimeout resolve ms))))

(defn do-stuff
  []
  (p/do!
   (println "Doing stuff which takes a while")
   (sleep 1000)
   1))

(p/let [a (do-stuff)
        b (inc a)
        c (do-stuff)
        d (+ b c)]
  (prn d))
$ nbb prom.cljs
Doing stuff which takes a while
Doing stuff which takes a while
3

Also see API docs.

Js-interop

Since nbb v0.0.75 applied-science/js-interop is available:

(ns example
  (:require [applied-science.js-interop :as j]))

(def o (j/lit {:a 1 :b 2 :c {:d 1}}))

(prn (j/select-keys o [:a :b])) ;; #js {:a 1, :b 2}
(prn (j/get-in o [:c :d])) ;; 1

Most of this library is supported in nbb, except the following:

  • destructuring using :syms
  • property access using .-x notation. In nbb, you must use keywords.

See the example of what is currently supported.

Examples

See the examples directory for small examples.

Also check out these projects built with nbb:

API

See API documentation.

Migrating to shadow-cljs

See this gist on how to convert an nbb script or project to shadow-cljs.

Build

Prequisites:

  • babashka >= 0.4.0
  • Clojure CLI >= 1.10.3.933
  • Node.js 16.5.0 (lower version may work, but this is the one I used to build)

To build:

  • Clone and cd into this repo
  • bb release

Run bb tasks for more project-related tasks.

Download Details:
Author: borkdude
Download Link: Download The Source Code
Official Website: https://github.com/borkdude/nbb 
License: EPL-1.0

#node #javascript

Jeremy  Reilly

Jeremy Reilly

1602805860

Create simple POS with React.js, Node.js, and MongoDB: Order Screen

Defenition:_ POS – “Point of Sale”. At the point of sale, the merchant calculates the amount owed by the customer, indicates that amount, may prepare an invoice for the customer (which may be a cash register printout), and indicates the options for the customer to make payment._

In the previous chapter, we worked on role-based access control feature for our react app. We had two roles: admin and employee. We used those user roles for conditional rendering with the react-rbac-guard package.

In this chapter, we are going to create an order page. The order page displays the products and the calculator to help calculate the total price. Finally, we will save the transaction to the database.

For the order page, the idea is to have to columns: lefts to display products and right to display total price and products in the cart.

Displaying Products

First, we are going to create a column that displays the number of products for sale. We are going to display them in a grid style by creating a new component called order.js. Now, we will create a file named create.js and work on it.

In create.js, we need to import the required component, hooks, and product actions as displayed in the code snippet below:

import  React,   {    useEffect   }    from    "react";

import   {    useSelector,    useDispatch   }    from    "react-redux";

 import   *    as   productActions  from    "../../actions/product.action";

export  default   ( props)   = > {}

Then, we fetch the product data using useDispatch hook variable inside the useEffect hook as directed in the code snippet below:

 const    dispatch   =   useDispatch();

useEffect(()   = > {

     dispatch( productActions.Index());

   },   []);

Next, we need to import a reducer named productReducer using useSelector hook in order to get the getting product data as displayed in the code snippet below:

 const    productReducer   =   useSelector(({    productReducer   })   = >  productReducer);

Now, we need to create a function to fetch all products. First, we create a product catalog by wrapping it in the card element and using the classes to show four-card items in a row. Each card will have the data concerning a single product. There will also be a button to add the items to the cart. The overall coding implementation of the function is provided in the code snippet below:


 const    renderProductRows   =   ()   = > {

      if   ( productReducer. result)   {

        const   {    result   }   =    productReducer;

        return   (

         <div className= "row" >

           { result   &&

            result.map((item, index) => {

              return (

                <>

      {index % 3 === 0 && <div class="w-100 d-lg-none mt-4"></div>}

                  <div class="col-md-6 col-lg-4 col-xl-3 py-2">

                    <div className="card h-100">

                      <img

                        className="card-img-top img-fluid"

                        src={

                          process.env.REACT_APP_PRODUCT_IMAGE_PATH +

                          "/" +

                          item.image

                        }

                        alt="Card image cap"

                      />

                      <div className="card-block">

                        <h4 className="card-title">{item.name}</h4>

                        <p className="card-text">Price {item.price}</p>

                        <p className="card-text">

                          <small className="text-muted">

                            remain {item.stock}

                          </small>

                        </p>

                       <a href="#" class="btn btn-primary btn-block ">

                          Add to Card

                        </a>                      

</div>

                    </div>

                  </div>

                </>

              );

             })}

         </ div >

       );

     }    else   {

        return    "loading...";

     }

   };

#javascript #node.js #pos tutorial #react #node

Wiley  Mayer

Wiley Mayer

1603447200

Create simple POS with React.js, Node.js, and MongoDB #17: Stat screen

Defenition:_ POS – “Point of Sale”. At the point of sale, the merchant calculates the amount owed by the customer, indicates that amount, may prepare an invoice for the customer (which may be a cash register printout), and indicates the options for the customer to make payment._

In the previous chapter, we implemented the order page in our POS project. We successfully displayed the products and calculate the total price along with a calculator to calculate the change to be returned. Finally, each order transaction was saved to the database. This was one of the complex parts of our tutorial that we successfully tackled.

Now, we are going to implement the final chapter for this tutorial series where we are implementing a graphical representation section on our dashboard screen. In the dashboard screen, we are going o display the statistics from the database using the react-chart.js library. The main aim here is to show you how to add graphs to represent visual data in the React app that already uses redux as functionality.

So, let us get started!

Prepare data from the backend

first, we create a new endpoint for send stat data create a new file name api_state.js inside this file we add a function for fetching data from the product table

const express = require( “express”);

const router = express.Router();

const product = require( “./models/product_schema”);

router.get( “/stat/current_inventory”, async ( req, res) = > {

try {

await product.find({}).exec( function ( err, data) {

if ( err) {

console.log( err);

} else {

res.json({

result: “success”,

message: “Fetch product Successfully”,

data: data,

});

}

});

} catch ( err) {

res.json({ result: “error”, message: err. msg });

}

});

module. exports = router;

Next, we need to register the API endpoint to api.js using use middleware function provided by express library as shown in the code snippet below:

const express = require( “express”);

const router = express.Router();

require( “./db”);

router. use(require( “./api_stat”));

module. exports = router;

Thus, we are done on the backend. Now, we can move forward to implement our frontend which will include a chart diagram on the dashboard screen.

Installing Dependencies

In order to configure and display charts in our react app, we need to install some dependencies that we will make it possible. The required libraries are chart.js and react-chartjs-2 which we can install by running the following command in our project terminal:

1

yarn add react- chartjs-2 chart. js

Next, we need to import the chart components such as Bar, Doughnut, etc. to the dashboard.js file from react-chartjs-2 library as directed in the code snippet below:

1

import { Bar, Doughnut , Line } from “react-chartjs-2”;

Configuring Chart

Here, we are going to configure the chart by using the data that we are going to fetch from the API endpoint that we created earlier. We are going to use redux methodologies for getting the chart data as well. Hence, we need to create constant states first.

Defining Constants

Here, we are defining some constants for the configuring redux mechanism for the chart as shown in the code snippet below:

1

2

3

export const STAT_FETCHING = “STAT_FETCHING”;

export const STAT_SUCCESS = “STAT_SUCCESS”;

export const STAT_FAILED = “STAT_FAILED”;

Creating Reducer

Next, we need to create a reducer in order to access the Redux store. The code required to implement a reducer for the redux mechanism is provided in the code snippet below:

import { STAT_FETCHING, STAT_SUCCESS, STAT_FAILED } from “…/constants”;

const initialState = {

isFetching: false,

isError: false,

result: null,

};

export default ( state = initialState, { type, payload }) = > {

switch ( type) {

case STAT_FETCHING:

return { … state, isFetching: true, isError: false, result: null };

case STAT_FAILED:

return { … state, isFetching: false, isError: true, result: null };

case STAT_SUCCESS:

return { … state, isFetching: false, isError: false, result: payload };

default:

return state;

}

};

Creating Reducer

Next, we need to create a reducer in order to access the Redux store. The code required to implement a reducer for the redux mechanism is provided in the code snippet below:

JavaScript

import statReducer from “./stat.reducer”;

export default combineReducers({

statReducer,

});

#javascript #node.js #pos tutorial #react

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