wip chapter 7

07-creational-design-patterns/07-revealing-constructor-immutable-buffer/README.md

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+# 07-revealing-constructor-immutable-buffer
+
+This example demonstrate how to use the revealing constructor pattern to
+implement an immutable buffer.
+
+## Run
+
+To run the example launch:
+
+```bash
+node index.js
+```

07-creational-design-patterns/07-revealing-constructor-immutable-buffer/immutableBuffer.js

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+const MODIFIER_NAMES = ['swap', 'write', 'fill']
+
+export class ImmutableBuffer {
+  constructor(size, executor) {
+    const buffer = Buffer.alloc(size)
+    const modifiers = {}
+    for (const prop in buffer) {
+      if (typeof buffer[prop] !== 'function') {
+        continue
+      }
+
+      if (MODIFIER_NAMES.some(m => prop.startsWith(m))) {
+        modifiers[prop] = buffer[prop].bind(buffer)
+      } else {
+        this[prop] = buffer[prop].bind(buffer)
+      }
+    }
+
+    executor(modifiers)
+  }
+}

07-creational-design-patterns/07-revealing-constructor-immutable-buffer/index.js

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+import { ImmutableBuffer } from './immutableBuffer.js'
+
+const hello = 'Hello!'
+const immutable = new ImmutableBuffer(hello.length, ({ write }) => {
+  write(hello)
+})
+
+console.log(String.fromCharCode(immutable.readInt8(0)))
+
+// the following line will throw
+// "TypeError: immutable.write is not a function"
+
+// immutable.write('Hello?')

07-creational-design-patterns/07-revealing-constructor-immutable-buffer/package.json

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+{
+  "name": "07-revealing-constructor-immutable-buffer",
+  "version": "1.0.0",
+  "description": "This example demonstrate how to use the revealing constructor pattern to implement an immutable buffer",
+  "type": "module",
+  "scripts": {},
+  "engines": {
+    "node": ">=22"
+  },
+  "engineStrict": true,
+  "keywords": [],
+  "author": "Luciano Mammino and Mario Casciaro",
+  "license": "MIT",
+  "dependencies": {}
+}

07-creational-design-patterns/08-singleton-false-uniqueness/.gitignore

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+!/node_modules/
+!/node_modules/*/node_modules

07-creational-design-patterns/08-singleton-false-uniqueness/README.md

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+# 08-singleton-false-uniqueness
+
+This example demonstrate how under certain conditions, an instance exported by a
+module stops to be a Singleton.
+
+## Run
+
+To run the example launch:
+
+```bash
+node index.js
+```
+
+NOTE: Don't run `npm install` or the since this sample is composed of some fake
+dependencies which otherwise might be overwritten.

07-creational-design-patterns/08-singleton-false-uniqueness/index.js

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+import { getDbInstance as getDbFromA } from 'package-a'
+import { getDbInstance as getDbFromB } from 'package-b'
+
+const isSame = getDbFromA() === getDbFromB()
+console.log(
+  `Is the db instance in package-a the same as package-b? ${isSame ? 'YES' : 'NO'}`
+)

07-creational-design-patterns/08-singleton-false-uniqueness/package.json

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+{
+  "name": "08-singleton-false-uniqueness",
+  "version": "1.0.0",
+  "description": "This example demonstrate how under certain conditions, an instance exported by a module stops to be a Singleton",
+  "type": "module",
+  "scripts": {},
+  "engines": {
+    "node": ">=22"
+  },
+  "engineStrict": true,
+  "keywords": [],
+  "author": "Luciano Mammino and Mario Casciaro",
+  "license": "MIT",
+  "dependencies": {}
+}

07-creational-design-patterns/09-singleton-dependencies/.gitignore

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+data.sqlite

07-creational-design-patterns/09-singleton-dependencies/README.md

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+# 09-singleton-dependencies
+
+This example shows how to wire dependencies using the singleton pattern
+
+## Dependencies
+
+Install all necessary dependencies with:
+
+```shell script
+npm install
+```
+
+## Run
+
+To run the example:
+
+```shell script
+node import-posts.js
+node index.js
+```

07-creational-design-patterns/09-singleton-dependencies/blog.js

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+import { db } from './db.js'
+
+export class Blog {
+  initialize() {
+    const initQuery = `CREATE TABLE IF NOT EXISTS posts (
+      id TEXT PRIMARY KEY,
+      title TEXT NOT NULL,
+      content TEXT,
+      created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+    );`
+
+    return db.run(initQuery)
+  }
+
+  createPost(id, title, content, createdAt) {
+    return db.run(
+      'INSERT INTO posts VALUES (?, ?, ?, ?)',
+      id,
+      title,
+      content,
+      createdAt
+    )
+  }
+
+  getAllPosts() {
+    return db.all('SELECT * FROM posts ORDER BY created_at DESC')
+  }
+}

07-creational-design-patterns/09-singleton-dependencies/db.js

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+import { join } from 'node:path'
+import { open } from 'sqlite'
+import sqlite3 from 'sqlite3'
+
+export const db = await open({
+  filename: join(import.meta.dirname, 'data.sqlite'),
+  driver: sqlite3.Database,
+})

07-creational-design-patterns/09-singleton-dependencies/import-posts.js

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+import { Blog } from './blog.js'
+
+const posts = [
+  {
+    id: 'my-first-post',
+    title: 'My first post',
+    content: 'Hello World!\nThis is my first post',
+    // biome-ignore lint/style/useNamingConvention: db mapping
+    created_at: new Date('2020-02-03'),
+  },
+  {
+    id: 'iterator-patterns',
+    title: 'Node.js iterator patterns',
+    content: "Let's talk about some iterator patterns in Node.js\n\n...",
+    // biome-ignore lint/style/useNamingConvention: db mapping
+    created_at: new Date('2020-02-06'),
+  },
+  {
+    id: 'dependency-injection',
+    title: 'Dependency injection in Node.js',
+    content:
+      'Today we will discuss about dependency injection in Node.js\n\n...',
+    // biome-ignore lint/style/useNamingConvention: db mapping
+    created_at: new Date('2020-02-29'),
+  },
+  // ...
+]
+
+const blog = new Blog()
+await blog.initialize()
+
+await Promise.all(
+  posts.map(post =>
+    blog.createPost(post.id, post.title, post.content, post.created_at)
+  )
+)
+console.log('All posts imported')

07-creational-design-patterns/09-singleton-dependencies/index.js

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+import { Blog } from './blog.js'
+
+const blog = new Blog()
+await blog.initialize()
+const posts = await blog.getAllPosts()
+if (posts.length === 0) {
+  console.log(
+    'No post available. Run `node import-posts.js`' +
+      ' to load some sample posts'
+  )
+}
+
+for (const post of posts) {
+  console.log(post.title)
+  console.log('-'.repeat(post.title.length))
+  console.log(`Published on ${new Date(post.created_at).toISOString()}`)
+  console.log(post.content)
+}

07-creational-design-patterns/09-singleton-dependencies/package.json

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+{
+  "name": "09-singleton-dependencies",
+  "version": "1.0.0",
+  "description": "This example shows how to wire dependencies using the singleton pattern",
+  "type": "module",
+  "scripts": {},
+  "engines": {
+    "node": ">=22"
+  },
+  "engineStrict": true,
+  "keywords": [],
+  "author": "Luciano Mammino and Mario Casciaro",
+  "license": "MIT",
+  "dependencies": {
+    "sqlite": "^5.1.1",
+    "sqlite3": "^5.1.7"
+  }
+}