Học Web3.js từ A-Z: Web3 Provider - Sử dụng Hook | useContext

Mastering Web3 | Web3 Provider - Sử dụng Hook | useContext

Khoá học cung cấp toàn bộ kiến thức Web3js qua thực hành để mọi người có thể thực hiện vô các dự án của các bạn một cách hiệu quả hơn, Dự án được xây dựng trên Nextjs và Javascript, ứng dụng React và React Hook để tối ưu hoá code.

source code: https://github.com/vugomars/web3-project-course/commit/5e2b1f12588549844253c218de3ba3cc09c62e2c 

#blockchain #solidity #smartcontract #react #web3

What is GEEK

Buddha Community

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:

• c64core: retrocompute aesthetics twitter bot
• gallery.cljs: script to download walpapers from windowsonearth.org.
• nbb-action-example: example of a Github action 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

Học Web3.js từ A-Z: Web3 Provider - Sử dụng Hook | useContext

Mastering Web3 | Web3 Provider - Sử dụng Hook | useContext

Khoá học cung cấp toàn bộ kiến thức Web3js qua thực hành để mọi người có thể thực hiện vô các dự án của các bạn một cách hiệu quả hơn, Dự án được xây dựng trên Nextjs và Javascript, ứng dụng React và React Hook để tối ưu hoá code.

source code: https://github.com/vugomars/web3-project-course/commit/5e2b1f12588549844253c218de3ba3cc09c62e2c 

#blockchain #solidity #smartcontract #react #web3

A Look at an ES2022 Feature: Class Static Initialization Blocks

ECMAScript class static initialization blocks

Class static blocks provide a mechanism to perform additional static initialization during class definition evaluation.

This is not intended as a replacement for public fields, as they provide useful information for static analysis tools and are a valid target for decorators. Rather, this is intended to augment existing use cases and enable new use cases not currently handled by that proposal.

Status

Stage: 4
Champion: Ron Buckton (@rbuckton)

For detailed status of this proposal see TODO, below.

Authors

• Ron Buckton (@rbuckton)

Motivations

The current proposals for static fields and static private fields provide a mechanism to perform per-field initialization of the static-side of a class during ClassDefinitionEvaluation, however there are some cases that cannot be covered easily. For example, if you need to evaluate statements during initialization (such as try..catch), or set two fields from a single value, you have to perform that logic outside of the class definition.

// without static blocks:
class C {
  static x = ...;
  static y;
  static z;
}

try {
  const obj = doSomethingWith(C.x);
  C.y = obj.y
  C.z = obj.z;
}
catch {
  C.y = ...;
  C.z = ...;
}

// with static blocks:
class C {
  static x = ...;
  static y;
  static z;
  static {
    try {
      const obj = doSomethingWith(this.x);
      this.y = obj.y;
      this.z = obj.z;
    }
    catch {
      this.y = ...;
      this.z = ...;
    }
  }
}

In addition, there are cases where information sharing needs to occur between a class with an instance private field and another class or function declared in the same scope.

Static blocks provide an opportunity to evaluate statements in the context of the current class declaration, with privileged access to private state (be they instance-private or static-private):

let getX;

export class C {
  #x
  constructor(x) {
    this.#x = { data: x };
  }

  static {
    // getX has privileged access to #x
    getX = (obj) => obj.#x;
  }
}

export function readXData(obj) {
  return getX(obj).data;
}

Relation to "Private Declarations"

The Private Declarations proposal also intends to address the issue of privileged access between two classes, by lifting the private name out of the class declaration and into the enclosing scope. While there is some overlap in that respect, private declarations do not solve the issue of multi-step static initialization without potentially exposing a private name to the outer scope purely for initialization purposes:

// with private declarations
private #z; // exposed purely for post-declaration initialization
class C {
  static y;
  static outer #z;
}
const obj = ...;
C.y = obj.y;
C.#z = obj.z;

// with static block
class C {
  static y;
  static #z; // not exposed outside of class
  static {
    const obj = ...;
    this.y = obj.y;
    this.#z = obj.z;
  }
}

In addition, Private Declarations expose a private name that potentially allows both read and write access to shared private state when read-only access might be desireable. To work around this with private declarations requires additional complexity (though there is a similar cost for static{} as well):

// with private declarations
private #zRead;
class C {
  #z = ...; // only writable inside of the class
  get #zRead() { return this.#z; } // wrapper needed to ensure read-only access
}

// with static
let zRead;
class C {
  #z = ...; // only writable inside of the class
  static { zRead = obj => obj.#z; } // callback needed to ensure read-only access
}

In the long run, however, there is nothing that prevents these two proposals from working side-by-side:

private #shared;
class C {
  static outer #shared;
  static #local;
  static {
    const obj = ...;
    this.#shared = obj.shared;
    this.#local = obj.local;
  }
}
class D {
  method() {
    C.#shared; // ok
    C.#local; // no access
  }
}

Prior Art

• C#: Static Constructors
• Java: Static Initializers

Syntax

class C {
  static {
    // statements
  }
}

Semantics

• A static {} initialization block creates a new lexical scope (e.g. var, function, and block-scoped declarations are local to the static {} initialization block. This lexical scope is nested within the lexical scope of the class body (granting privileged access to instance private state for the class).
• A class may have any number of static {} initialization blocks in its class body.
• static {} initialization blocks are evaluated in document order interleaved with static field initializers.
• A static {} initialization block may not have decorators (instead you would decorate the class itself).
• When evaluated, a static {} initialization block's this receiver is the constructor object of the class (as with static field initializers).
• It is a Syntax Error to reference arguments from within a static {} initialization block.
• It is a Syntax Error to include a SuperCall (i.e., super()) from within a static {} initialization block.
• A static {} initialization block may contain SuperProperty references as a means to access or invoke static members on a base class that may have been overridden by the derived class containing the static {} initialization block.
• A static {} initialization block should be represented as an independent stack frame in debuggers and exception traces.

Examples

// "friend" access (same module)
let A, B;
{
  let friendA;

  A = class A {
    #x;

    static {
        friendA = {
          getX(obj) { return obj.#x },
          setX(obj, value) { obj.#x = value }
        };
    }
  };

  B = class B {
    constructor(a) {
      const x = friendA.getX(a); // ok
      friendA.setX(a, x); // ok
    }
  };
}

References

• Stage 0 Presentation

TODO

The following is a high-level list of tasks to progress through each stage of the TC39 proposal process:

Stage 1 Entrance Criteria

• Identified a "champion" who will advance the addition.
• Prose outlining the problem or need and the general shape of a solution.
• Illustrative examples of usage.
• High-level API.

Stage 2 Entrance Criteria

• Initial specification text.
• Transpiler support (Optional).
  • Babel v7.12.0
  • TypeScript v4.4 beta (TypeScript Playground)

Stage 3 Entrance Criteria

• Complete specification text.
• Designated reviewers have signed off on the current spec text.
• The ECMAScript editor has signed off on the current spec text.

Stage 4 Entrance Criteria

For up-to-date information on Stage 4 criteria, check: #48

• Test262 acceptance tests have been written for mainline usage scenarios and merged.
• Two compatible implementations which pass the acceptance tests:
  • SpiderMonkey — Partially shipping Shipping behind a flag in 92, Intent to ship unflagged in 93: 
    
  • V8 — Shipping unflagged (at least as of 9.4.146): 
    
• A pull request has been sent to tc39/ecma262 with the integrated spec text.
• The ECMAScript editor has signed off on the pull request.

Download Details:
Author: tc39
The Demo/Documentation: View The Demo/Documentation
Download Link: Download The Source Code
Official Website: https://github.com/tc39/proposal-class-static-block 
License: BSD-3
#javascript #es2022 #ecmascript 

Học Web3.js từ A-Z: LoadProvider - Lấy và sử dụng dữ liệu từ Web3

Mastering Web3 | LoadProvider - Lấy và sử dụng dữ liệu từ Web3

Khoá học cung cấp toàn bộ kiến thức Web3js qua thực hành để mọi người có thể thực hiện vô các dự án của các bạn một cách hiệu quả hơn, Dự án được xây dựng trên Nextjs và Javascript, ứng dụng React và React Hook để tối ưu hoá code.

Source code: https://github.com/vugomars/web3-project-course/commit/9b0f1da5d85ac3d0977c6da31f75ae2fd60becdc 

#blockchain #solidity #smartcontract #web3 #react

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