Kriza Educa

Kriza Educa

1594267904

How to Build a Single Page Application (SPA) Site with JavaScript (Vanilla.js)

Modern JavaScript frameworks exist to address deficiencies in the capabilities provided out of the box by HTML5, JavaScript, CSS, and WebAssembly. The latest stable version of JavaScript (ECMAScript® 2015) evolved significantly compared to earlier versions, with better control over scope, powerful string manipulation capabilities, destructuring, parameter enhancements, and the built-in implementation of classes and modules (there is no longer a need to use IIFEs or immediately-invoked function expressions). The purpose of this post is to explore how to build modern apps using the latest JavaScript features.

The Project

I implemented a Single Page Application (SPA) app based completely on pure JavaScript (“Vanilla.js”). It includes routing (you can bookmark and navigate pages), databinding, reusable web components and uses JavaScript’s native module functionality.

#vanilla.js #javascript #spa

What is GEEK

Buddha Community

How to Build a Single Page Application (SPA) Site with JavaScript (Vanilla.js)

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

Kriza Educa

Kriza Educa

1594267904

How to Build a Single Page Application (SPA) Site with JavaScript (Vanilla.js)

Modern JavaScript frameworks exist to address deficiencies in the capabilities provided out of the box by HTML5, JavaScript, CSS, and WebAssembly. The latest stable version of JavaScript (ECMAScript® 2015) evolved significantly compared to earlier versions, with better control over scope, powerful string manipulation capabilities, destructuring, parameter enhancements, and the built-in implementation of classes and modules (there is no longer a need to use IIFEs or immediately-invoked function expressions). The purpose of this post is to explore how to build modern apps using the latest JavaScript features.

The Project

I implemented a Single Page Application (SPA) app based completely on pure JavaScript (“Vanilla.js”). It includes routing (you can bookmark and navigate pages), databinding, reusable web components and uses JavaScript’s native module functionality.

#vanilla.js #javascript #spa

Paresh Sagar

1581940975

What Is A Single-Page Application?

Single page web apps are an ideal choice when thinking about future web development. This architecture is a perfect choice for social networks stuff, SaaS platforms, or some close communities where SEO doesn’t matter.

#what is a single page application #single page application #single page application development

Tanya  Shields

Tanya Shields

1597747920

Creating a precise countdown with Vanilla JS

Image for post

On a recent technical interview I had for a big tech company, in one of the steps of the process I was asked the following:

Create a countdown from 1:30 to zero using plain javascript and HTML, and that’s all.

“Cool”, I said to myself, that’s something I can achieve easily. The total time I had to develop that was 45 minutes, which at first looked more than enough.

I started doing the simplest thing I could imagine, mimicking what a normal clock or countdown does: at each 1-second interval, we would decrease the value of the counter by 1 until the end of the 90-second period. This was the result:

const initialSeconds = 90;

let remainingSeconds;
/**
* Returns seconds in format mm:ss
* @param {Number} seconds
* @return {string}
*/
const formatMinutesSeconds = (seconds) => {
    const thisDate = new Date(seconds * 1000);
    return `${thisDate.getMinutes()}:${thisDate.getSeconds()}`;
};
/**
* Renders the remaining time in a format mm:ss
* @param {Number} seconds
*/
const renderCountdown = seconds => {
    const counterElement = document.getElementById('counter');
    const stringCounter = formatMinutesSeconds(seconds);
    counterElement.innerText = stringCounter;
};
/**
* Starts a countdown with the given seconds
* @param {Number} seconds
*/
const startCountdown = (seconds) => {
    remainingSeconds = seconds;
    setInterval(_ => {
        if (remainingSeconds > 0) {
            remainingSeconds--;
            renderCountdown(remainingSeconds);
        }
    }, 1000);
    renderCountdown(remainingSeconds);
};
startCountdown(initialSeconds);

As you can see, I used the native setInterval function to mimic a tick on a regular clock, and decreased the total amount of seconds by 1. By that time, around 10–15 minutes had passed and the interviewer told me:

Well done, but do you think it will be precise enough?

As you may know (or not), Javascript works with a single thread with no context switching, which in other words, means that functions are executed from the beginning until the end without interruptions, so, if there was another function somewhere taking a lot of time (let’s say a long for statement), it would cause some delays. Using a setInterval, will only guarantee that the callback function will be executed at least n seconds after the time is created, but if the Event Loop is busy at the moment of its completion, it will wait until it finishes all the previous tasks before running the code we want.

#js #vanilla-javascript #vanillajs #javascript-interview #javascript #programming

Franz  Becker

Franz Becker

1624522860

Single Page Apps: Placebo Junk?

SPA’s are wildly popular right now, with the fans of such site and application building starting to sound more like cultists than rational adults. This figures as there’s significant overlap between the cheesy framework fanboys and those making wild unfounded claims about how much “better” SPA are for user experience.

Sadly much like artists under the delusion that they are designers, those making these UX claims know just as little about user experience or accessibility.

As I’ve said many the time, front-end framework fans are devoid of the most basic knowledge of what HTML and CSS are even for; thus it’s no shock they have the same cult-like attitude when it comes to throwing “JavaScript for nothing” at websites.

Though MOST of the problems are not the concept of SPA’s fault. No, the blame lies at the implementation’s doorstep.

Implementation Woes

How an SPA is created and coded is where most of it goes wrong. Let’s go through some of the most common problems.

#javascript #css #html #single-page-applications #web-development #single page apps