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API Reference

Documentation

• 📚 Full Documentation - Complete guide with examples
• 🔧 API Reference - You’re here!
• ⚡ Cheatsheet - Quick recipes and code snippets

Public API Surface

The API instance exposes these public properties and methods:

• api.use(plugin, options) - Install plugins with optional configuration
• api.customize(config) - Add hooks, methods, vars, and helpers after initialization
• api.addScope(name, options, extras) - Add scopes with configuration and optional customizations
• api.setScopeAlias(aliasName, addScopeAlias) - Create aliases for the scopes property and addScope method
• api.scopes - Access to defined scopes (e.g., api.scopes.users.get())
• api.[aliasName] - If setScopeAlias was called (e.g., api.tables for database APIs)
• api.[addScopeAlias] - If setScopeAlias was called with second parameter (e.g., api.addTable)
• api.[methodName]() - Direct calls to defined API methods
• api.options - Read-only access to the API configuration (includes name, version, and merged logging config)

Static Methods

• Api.registry.get(name, version) - Get a registered API instance
• Api.registry.list() - List all registered APIs and their versions
• Api.registry.has(name, version) - Check if an API is registered
• Api.registry.versions(name) - Get all versions of a specific API

Handler Context Reference

Global API Methods

When you define an API method (via apiMethods in customize or via plugin), the handler receives:

// Handler signature for global API methods:
async ({ 
  params,         // Parameters passed to the method call
  context,        // Mutable object for passing data between hooks
  vars,           // Variables proxy
  helpers,        // Helpers proxy
  scope,          // null (no current scope for global methods)
  scopes,         // Access to all scopes (api.scopes)
  runHooks,       // Function to run hooks: runHooks(hookName)
  log,            // Logger instance for this context
  name,           // The method name being called
  apiOptions,     // Frozen API configuration {name, version, ...}
  pluginOptions,  // Frozen plugin configurations {pluginName: options, ...}
  // If setScopeAlias was called:
  [aliasName]     // Same as 'scopes' but with custom name (e.g., 'tables')
}) => {
  // Implementation
  await runHooks('beforeProcess');
  const result = await doSomething(params);
  context.result = result;
  await runHooks('afterProcess');
  return context.result;
}

Scope Methods

When you define a scope method (via scopeMethods in customize or via plugin), the handler receives:

// Handler signature for scope methods:
async ({ 
  params,          // Parameters passed to the method call
  context,         // Mutable object for passing data between hooks
  vars,            // Variables proxy (merged: global + scope vars)
  helpers,         // Helpers proxy (merged: global + scope helpers)
  scope,           // Current scope object (e.g., api.scopes.users)
  scopes,          // All scopes proxy (api.scopes)
  runHooks,        // Function to run hooks: runHooks(hookName)
  log,             // Logger instance for this context
  name,            // The method name being called
  apiOptions,      // Frozen API configuration {name, version, ...}
  pluginOptions,   // Frozen plugin configurations {pluginName: options, ...}
  scopeOptions,    // Frozen scope-specific options (passed to addScope)
  scopeName,       // Current scope name as string (e.g., 'users')
  // If setScopeAlias was called:
  [aliasName]      // Same as 'scopes' but with custom name (e.g., 'tables')
}) => {
  // Implementation
  console.log(`Called ${name} on scope ${scopeName}`);
  
  // Can call other methods on current scope directly:
  await scope.validate(params);
  
  // Or access other scopes:
  const relatedData = await scopes.related.get({ id: params.relatedId });
  
  return processData(params, scopeOptions);
}

Example: Using Scope Aliases

api.setScopeAlias('tables');

// Now in handlers:
async ({ params, scope, scopes, tables, scopeName }) => {
  // 'tables' is the same as 'scopes'
  // 'scope' is the current scope object
  
  // Clean, domain-specific syntax:
  await scope.validate(params);  // Validate current table
  await tables.orders.get({ userId: params.id });  // Access orders table
}

Hook Handlers

Hook handlers receive a different parameter name for user data:

// Hook handler signature (when added via plugin or customize):
async ({ 
  methodParams,    // The params passed to the original method call
  context,         // The context object from the method (mutable, shared between hooks)
  vars,            // Variables (scope-aware if hook run with scope)
  helpers,         // Helpers (scope-aware if hook run with scope)
  scope,           // Current scope object if hook run in scope context, null otherwise
  scopes,          // All scopes proxy (api.scopes)
  runHooks,        // Function to run hooks (careful of recursion!)
  log,             // Logger instance for this context
  name,            // Hook name (e.g., 'beforeFetch', 'afterFetch')
  apiOptions,      // Frozen API configuration
  pluginOptions,   // Frozen plugin configurations
  scopeOptions,    // Frozen scope options (only if hook run with scope)
  scopeName,       // Scope name or null
  // If setScopeAlias was called:
  [aliasName]      // Same as 'scopes' but with custom name
}) => {
  // Hook handler implementation
  console.log(`Hook ${name} called with params:`, methodParams);
  
  // Modify context to share data with other hooks or the method
  context.processedBy = context.processedBy || [];
  context.processedBy.push(name);
  
  // Return false to stop the hook chain
  if (context.skipRemaining) {
    return false;
  }
}

Important Notes on Hooks:

• Hooks receive methodParams instead of params to distinguish from method handlers
• The context object is shared between all hooks and the method
• Returning false from a hook stops the execution of remaining hooks in the chain
• Hooks can be global (run for all scopes) or scope-specific

Plugin System

Plugin Structure

const myPlugin = {
  name: 'myPlugin',              // Required: unique plugin name
  dependencies: ['otherPlugin'], // Optional: array of required plugin names
  install: (installContext) => { // Required: installation function
    // Plugin setup code
  }
};

Plugin Install Context

The install function receives a context object with these properties:

install: ({
  // Setup methods
  addApiMethod,       // Function to add global API methods
  addScopeMethod,     // Function to define scope methods
  addScope,           // Function to add scopes
  setScopeAlias,      // Function to create scope aliases
  
  // Hook management
  addHook,            // Special function that auto-injects plugin name:
                      // addHook(hookName, functionName, hookOptions, handler)
  
  // Event management
  on,                 // Register event listeners:
                      // on(eventName, listenerName, handler)
  
  // Data access
  vars,               // Variables proxy (mutable)
  helpers,            // Helpers proxy (mutable)
  scopes,             // Access to all scopes
  
  // Logging
  log,                // Logger instance for this plugin context
  
  // Plugin metadata
  name,               // Plugin name (same as plugin.name)
  apiOptions,         // Frozen API configuration
  pluginOptions,      // Frozen plugin configurations
  context,            // Empty context object for plugin use
  
  // API instance
  api                 // The API instance itself (to define more properties)
}) => {
  // Example usage:
  
  // Add a global method
  addApiMethod('getData', async ({ params, vars, helpers }) => {
    return await helpers.fetch(params.url);
  });
  
  // Add a scope method
  addScopeMethod('validate', async ({ params, scopeOptions }) => {
    return validateAgainstSchema(params, scopeOptions.schema);
  });
  
  // Add a hook
  addHook('beforeFetch', 'addAuth', {}, async ({ context, vars }) => {
    context.headers = { ...context.headers, Authorization: vars.apiKey };
  });
  
  // Set variables
  vars.apiKey = 'default-key';
  
  // Add helpers
  helpers.fetch = async (url) => {
    // Custom fetch implementation
  };
  
  // Use the API instance for advanced operations
  // For example, creating a namespace programmatically:
  // api.namespace('myNamespace').addApiMethod('customMethod', handler);
}

Using Plugins

// Install a plugin
api.use(myPlugin);

// Install with options
api.use(myPlugin, {
  apiKey: 'custom-key',
  endpoint: 'https://api.example.com'
});

// Options are available in handlers via pluginOptions
async ({ pluginOptions }) => {
  const options = pluginOptions.myPlugin; // { apiKey: 'custom-key', ... }
}

Event System

Overview

The event system provides lifecycle notifications separate from the hook system. While hooks intercept and can modify behavior, events are fire-and-forget notifications about system changes.

Event Registration

Plugins can register event listeners using the on method in their install context:

const myPlugin = {
  name: 'my-plugin',
  install({ on }) {
    // on(eventName, listenerName, handler)
    on('scope:added', 'handleNewScope', async (eventContext) => {
      console.log(`Scope ${eventContext.eventData.scopeName} was added`);
    });
  }
};

Event Handler Context

Event handlers receive a context object with:

{
  eventName: string,        // The event that was triggered
  eventData: Object,        // Event-specific data (see events below)
  api: {                    // Read-only API access
    vars: Proxy,            // API variables (proxy)
    helpers: Proxy,         // API helpers (proxy)
    scopes: Proxy,          // All scopes
    options: Object,        // Frozen API options
    pluginOptions: Object   // Frozen plugin options
  },
  log: Logger              // Context-specific logger
}

Available Events

scope:added

Emitted after a scope is successfully added to the API.

eventData: {
  scopeName: string,      // Name of the added scope
  scopeOptions: Object,   // Options passed to addScope
  scopeExtras: Object     // Extras (hooks, methods, etc.) passed to addScope
}

method:api:added

Emitted after an API method is added.

eventData: {
  methodName: string,     // Name of the added method
  handler: Function       // The method handler function
}

method:scope:added

Emitted after a scope method template is added.

eventData: {
  methodName: string,     // Name of the added method
  handler: Function       // The method handler function
}

plugin:installed

Emitted after a plugin is successfully installed.

eventData: {
  pluginName: string,     // Name of the installed plugin
  pluginOptions: Object,  // Options passed to api.use()
  plugin: Object          // The plugin object itself
}

Event System Internals

The event system uses three private methods on the Api instance:

_on(eventName, pluginName, listenerName, handler)

Registers an event listener. Called automatically by the plugin install context’s on method.

_emit(eventName, eventData)

Emits an event to all registered listeners. Called internally when system changes occur.

_removeListener(eventName, listenerName)

Removes a specific event listener. Returns true if the listener was found and removed.

Error Handling

Event handler errors are isolated - they are logged but don’t propagate or stop execution:

on('scope:added', 'mightFail', async ({ eventData }) => {
  throw new Error('This error is logged but does not stop scope creation');
});

Best Practices

1. Use unique listener names - Makes debugging easier and allows specific removal
2. Keep handlers lightweight - Events run synchronously and can impact performance
3. Don’t rely on event ordering - While listeners execute in registration order, this shouldn’t be depended upon
4. Use events for side effects only - Events cannot cancel operations or modify behavior
5. Access API state read-only - While api.vars is technically mutable, avoid modifications that affect core behavior

Example: Comprehensive Event Plugin

const EventMonitorPlugin = {
  name: 'event-monitor',
  
  install({ on, addApiMethod, vars }) {
    // Initialize tracking
    vars.eventLog = [];
    
    // Register for all events
    on('scope:added', 'logScope', ({ eventData, api }) => {
      api.vars.eventLog.push({
        type: 'scope',
        name: eventData.scopeName,
        timestamp: Date.now()
      });
    });
    
    on('method:api:added', 'logApiMethod', ({ eventData, api }) => {
      api.vars.eventLog.push({
        type: 'api-method',
        name: eventData.methodName,
        timestamp: Date.now()
      });
    });
    
    on('plugin:installed', 'logPlugin', ({ eventData, api }) => {
      if (eventData.pluginName !== 'event-monitor') {
        api.vars.eventLog.push({
          type: 'plugin',
          name: eventData.pluginName,
          timestamp: Date.now()
        });
      }
    });
    
    // Expose the event log
    addApiMethod('getEventLog', async ({ vars }) => {
      return vars.eventLog;
    });
  }
};

Testing

Registry Management

The library maintains a global registry of API instances by name and version. For testing, you can reset this registry:

import { resetGlobalRegistryForTesting } from './index.js';

// In your test setup
beforeEach(() => {
  resetGlobalRegistryForTesting();
});

// Now you can create APIs with the same name/version in each test
test('my test', () => {
  const api = new Api({ name: 'test-api', version: '1.0.0' });
  // ... test code
});

Testing Best Practices

1. Reset the registry between tests to avoid conflicts
2. Use unique API names per test if running tests in parallel
3. Mock external dependencies in your plugins
4. Test hooks independently by creating minimal APIs

// Example: Testing a plugin
import { Api } from './index.js';

test('myPlugin adds expected functionality', async () => {
  const api = new Api({ name: 'test', version: '1.0.0' });
  
  const myPlugin = {
    name: 'test-plugin',
    install: ({ addApiMethod, vars }) => {
      vars.testValue = 'plugin-loaded';
      addApiMethod('getValue', async ({ vars }) => vars.testValue);
    }
  };
  
  api.use(myPlugin);
  
  const result = await api.getValue();
  expect(result).toBe('plugin-loaded');
});

Error Handling

The library exports several error classes that it throws in different scenarios. You can catch these for specific error handling:

Error Classes

All errors extend from HookedApiError which includes a code property for programmatic error handling.

ValidationError

Thrown when validation fails (invalid method names, scope names, parameters, etc.)

try {
  api.addScope('123-invalid-name', {});
} catch (error) {
  if (error instanceof ValidationError) {
    console.log(error.code);        // 'VALIDATION_ERROR'
    console.log(error.field);       // 'name'
    console.log(error.value);       // '123-invalid-name'
    console.log(error.validValues); // 'valid JavaScript identifier'
  }
}

Properties:

• field - The field that failed validation
• value - The invalid value provided
• validValues - Description of what’s expected

PluginError

Thrown when plugin operations fail (installation, dependencies, naming conflicts)

try {
  api.use({ name: 'api' }); // Reserved name
} catch (error) {
  if (error instanceof PluginError) {
    console.log(error.code);             // 'PLUGIN_ERROR'
    console.log(error.pluginName);       // 'api'
    console.log(error.installedPlugins); // ['other-plugin', ...]
  }
}

Properties:

• pluginName - The plugin that caused the error
• installedPlugins - Array of currently installed plugins

ConfigurationError

Thrown when API configuration is invalid (missing name, invalid version, etc.)

try {
  const api = new Api({ version: 'invalid' });
} catch (error) {
  if (error instanceof ConfigurationError) {
    console.log(error.code);     // 'CONFIGURATION_ERROR'
    console.log(error.received); // 'invalid'
    console.log(error.expected); // 'semver format (e.g., 1.0.0)'
    console.log(error.example);  // "{ version: '1.0.0' }"
  }
}

Properties:

• received - What was provided
• expected - What was expected
• example - Example of correct usage

ScopeError

Thrown when scope operations fail (scope not found, duplicate scope names)

try {
  await api.scopes.nonexistent.method();
} catch (error) {
  if (error instanceof ScopeError) {
    console.log(error.code);            // 'SCOPE_ERROR'
    console.log(error.scopeName);       // 'nonexistent'
    console.log(error.availableScopes); // ['users', 'posts', ...]
  }
}

Properties:

• scopeName - The scope that caused the error
• availableScopes - Array of available scope names

MethodError

Thrown when method operations fail (conflicts, invalid calls)

try {
  api.scopes.users(); // Direct scope call
} catch (error) {
  if (error instanceof MethodError) {
    console.log(error.code);       // 'METHOD_ERROR'
    console.log(error.methodName); // 'users'
    console.log(error.suggestion); // 'api.scopes.users.methodName()'
  }
}

Properties:

• methodName - The method that caused the error
• suggestion - Suggested correct usage

Importing Error Classes and Constants

import { 
  Api, 
  LogLevel,
  HookedApiError,
  ValidationError,
  PluginError,
  ConfigurationError,
  ScopeError,
  MethodError 
} from './index.js';

// Catch all library errors
try {
  // ... api operations
} catch (error) {
  if (error instanceof HookedApiError) {
    console.log('Library error:', error.code, error.message);
  }
}