Modern JavaScript

Static Initialization Blocks

Static blocks for complex class initialization (ES2022)

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What are Static Initialization Blocks? ⚙️

Run complex setup code when a class is first loaded! Static blocks let you execute statements during class initialization - perfect for complex setup logicthat doesn't fit in simple static field assignments.

Basic Syntax 📝

Run code when class loads

Simple Example

class DatabaseConnection {
  static connection;
  static isReady = false;
  
  // Static initialization block
  static {
    console.log('Initializing database connection...');
    
    // Complex setup logic here
    this.connection = {
      host: 'localhost',
      port: 5432,
      connected: true
    };
    
    this.isReady = true;
    console.log('Database ready!');
  }
}

// Output when class is first loaded:
// "Initializing database connection..."
// "Database ready!"

console.log(DatabaseConnection.isReady); // true
console.log(DatabaseConnection.connection); // { host: 'localhost', ... }

Multiple Static Blocks 🔢

Run several blocks in order

Execution Order

class Config {
  static data = {};
  
  static {
    console.log('Block 1: Loading config...');
    this.data.env = 'production';
  }
  
  static version = '1.0.0';
  
  static {
    console.log('Block 2: Setting up features...');
    this.data.features = ['auth', 'api'];
  }
  
  static {
    console.log('Block 3: Validation...');
    if (!this.data.env) {
      throw new Error('No environment set!');
    }
    console.log('Config validated!');
  }
}

// Output:
// "Block 1: Loading config..."
// "Block 2: Setting up features..."
// "Block 3: Validation..."
// "Config validated!"

Accessing Private Fields 🔒

Setup Private Static Fields

class APIClient {
  static #apiKey;
  static #endpoint;
  
  static {
    // Complex initialization for private fields
    console.log('Setting up API client...');
    
    // Read from environment or config
    this.#apiKey = 'secret-key-123';
    this.#endpoint = 'https://api.example.com';
    
    // Validate
    if (!this.#apiKey) {
      throw new Error('API key required!');
    }
    
    console.log('API client configured');
  }
  
  static getEndpoint() {
    return this.#endpoint;
  }
  
  static makeRequest(path) {
    return `${this.#endpoint}${path}?key=${this.#apiKey}`;
  }
}

console.log(APIClient.getEndpoint()); // 'https://api.example.com'
console.log(APIClient.makeRequest('/users')); 
// 'https://api.example.com/users?key=secret-key-123'

Real-World Example 🎯

Example: Feature Flags

class FeatureFlags {
  static #flags = new Map();
  static #initialized = false;
  
  static {
    console.log('Loading feature flags...');
    
    // Simulate loading from config
    const config = {
      newUI: true,
      betaFeatures: false,
      analytics: true
    };
    
    // Process and store
    for (const [key, value] of Object.entries(config)) {
      this.#flags.set(key, value);
      console.log(`  ${key}: ${value}`);
    }
    
    this.#initialized = true;
    console.log('Feature flags loaded!');
  }
  
  static isEnabled(feature) {
    if (!this.#initialized) {
      throw new Error('Flags not initialized!');
    }
    return this.#flags.get(feature) || false;
  }
  
  static listAll() {
    return Array.from(this.#flags.entries());
  }
}

// Automatic initialization when class loads!
console.log(FeatureFlags.isEnabled('newUI')); // true
console.log(FeatureFlags.isEnabled('betaFeatures')); // false

When to Use 🎯

Complex Setup Logic

When simple field assignment isn't enough - need loops, conditionals, try-catch

Private Field Setup

Initialize private static fields with complex logic

One-Time Setup

Configuration, connections, registrations that happen once when class loads

Quick Summary 📝

⚙️

Static Blocks

Run code when class is first loaded

🔒

Private Access

Can initialize private static fields

🎯

Complex Logic

Loops, conditionals, error handling

✨

ES2022

Modern class initialization

Previous Topic

Private Methods

Private instance and static methods with # syntax (ES2022).

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Top-Level Await

Using await at module top level without async wrapper (ES2022).

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Modern JavaScript

Static Initialization Blocks

Static blocks for complex class initialization (ES2022)

Find videos you like?

Save to resource drawer for future reference!

What are Static Initialization Blocks? ⚙️

Basic Syntax 📝

Run code when class loads

Simple Example

class DatabaseConnection {
  static connection;
  static isReady = false;
  
  // Static initialization block
  static {
    console.log('Initializing database connection...');
    
    // Complex setup logic here
    this.connection = {
      host: 'localhost',
      port: 5432,
      connected: true
    };
    
    this.isReady = true;
    console.log('Database ready!');
  }
}

// Output when class is first loaded:
// "Initializing database connection..."
// "Database ready!"

console.log(DatabaseConnection.isReady); // true
console.log(DatabaseConnection.connection); // { host: 'localhost', ... }

Multiple Static Blocks 🔢

Run several blocks in order

Execution Order

class Config {
  static data = {};
  
  static {
    console.log('Block 1: Loading config...');
    this.data.env = 'production';
  }
  
  static version = '1.0.0';
  
  static {
    console.log('Block 2: Setting up features...');
    this.data.features = ['auth', 'api'];
  }
  
  static {
    console.log('Block 3: Validation...');
    if (!this.data.env) {
      throw new Error('No environment set!');
    }
    console.log('Config validated!');
  }
}

// Output:
// "Block 1: Loading config..."
// "Block 2: Setting up features..."
// "Block 3: Validation..."
// "Config validated!"

Accessing Private Fields 🔒

Setup Private Static Fields

class APIClient {
  static #apiKey;
  static #endpoint;
  
  static {
    // Complex initialization for private fields
    console.log('Setting up API client...');
    
    // Read from environment or config
    this.#apiKey = 'secret-key-123';
    this.#endpoint = 'https://api.example.com';
    
    // Validate
    if (!this.#apiKey) {
      throw new Error('API key required!');
    }
    
    console.log('API client configured');
  }
  
  static getEndpoint() {
    return this.#endpoint;
  }
  
  static makeRequest(path) {
    return `${this.#endpoint}${path}?key=${this.#apiKey}`;
  }
}

console.log(APIClient.getEndpoint()); // 'https://api.example.com'
console.log(APIClient.makeRequest('/users')); 
// 'https://api.example.com/users?key=secret-key-123'

Real-World Example 🎯

Example: Feature Flags

class FeatureFlags {
  static #flags = new Map();
  static #initialized = false;
  
  static {
    console.log('Loading feature flags...');
    
    // Simulate loading from config
    const config = {
      newUI: true,
      betaFeatures: false,
      analytics: true
    };
    
    // Process and store
    for (const [key, value] of Object.entries(config)) {
      this.#flags.set(key, value);
      console.log(`  ${key}: ${value}`);
    }
    
    this.#initialized = true;
    console.log('Feature flags loaded!');
  }
  
  static isEnabled(feature) {
    if (!this.#initialized) {
      throw new Error('Flags not initialized!');
    }
    return this.#flags.get(feature) || false;
  }
  
  static listAll() {
    return Array.from(this.#flags.entries());
  }
}

// Automatic initialization when class loads!
console.log(FeatureFlags.isEnabled('newUI')); // true
console.log(FeatureFlags.isEnabled('betaFeatures')); // false

When to Use 🎯

Complex Setup Logic

When simple field assignment isn't enough - need loops, conditionals, try-catch

Private Field Setup

Initialize private static fields with complex logic

One-Time Setup

Configuration, connections, registrations that happen once when class loads

Quick Summary 📝

⚙️

Static Blocks

Run code when class is first loaded

🔒

Private Access

Can initialize private static fields

🎯

Complex Logic

Loops, conditionals, error handling

✨

ES2022

Modern class initialization

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Private Methods

Top-Level Await

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Static Initialization Blocks

What are Static Initialization Blocks? ⚙️

Simple Example

Execution Order

Setup Private Static Fields

Example: Feature Flags

Complex Setup Logic

Private Field Setup

One-Time Setup

Quick Summary 📝

Static Blocks

Private Access

Complex Logic

ES2022

Private Methods

Top-Level Await

JavaScript Code Editor

Static Initialization Blocks

What are Static Initialization Blocks? ⚙️

Simple Example

Execution Order

Setup Private Static Fields

Example: Feature Flags

Complex Setup Logic

Private Field Setup

One-Time Setup

Quick Summary 📝

Static Blocks

Private Access

Complex Logic

ES2022