A correlated subquery is used to reference columns from the outer query within the subquery. This allows the subquery to be evaluated once for each row processed by the outer query, enabling more complex filtering and calculations. 

Stored procedures can enhance performance in a DB2 environment in various ways. One key advantage is minimizing compilation overhead. By precompiling stored procedures, DB2 can save time during execution by avoiding the need to recompile the same SQL statements repeatedly. This reduces CPU usage and improves overall system performance. Additionally, stored procedures can optimize query execution by executing complex operations on the server side, reducing network traffic and improving response times for client applications. Thus, using stored procedures can significantly enhance performance in a DB2 environment. 

Triggers in DB2 can be classified based on their action, which specifies the event that triggers the execution of the trigger. Common actions include BEFORE and AFTER, determining whether the trigger fires before or after the triggering event. 

The DB2 event monitor captures information about SQL statements executed against the database. This includes details such as the execution time, resource usage, and the frequency of specific SQL statements. While buffer pool usage, database connections, and lock escalations are important metrics, they are not the primary focus of the event monitor. 

Query Monitor works in conjunction with Visual Explain for comprehensive query analysis. While Visual Explain provides a visual representation of the query execution plan, Query Monitor captures and analyzes actual SQL statements and their associated performance metrics, allowing for a deeper understanding of query performance and potential optimization opportunities. 

A try/catch block inside an async function can catch both synchronous errors (those that occur in the synchronous part of the code) and asynchronous errors (those that occur in asynchronous operations like Promises). This ensures robust error handling in async functions.

In ES6 classes, the constructor method is a special method used for creating and initializing objects within the class. It is automatically called when an object is instantiated from the class.

Symbol.for() is used to create symbols that are shared across different scopes. It searches for an existing symbol with the given key and returns it if found; otherwise, it creates a new one. Example: const sharedSymbol = Symbol.for('sharedKey');

Using an arrow function in a React class component's event handler can lead to better performance, as it avoids the need to bind "this" explicitly. However, it's essential to be cautious about potential memory leaks in certain scenarios.

In ES6, the extends keyword is used to create a subclass that inherits from a specified class. The subclass can then access the properties and methods of the parent class. This facilitates the concept of class inheritance in JavaScript.