Can you explain the difference between var, let, and const in JavaScript? Provide examples of when you would use each. Describe the event loop in JavaScript. How does it handle asynchronous calls? How do you ensure your JavaScript code is secure? Discuss some common security vulnerabilities and how to prevent them. What are JavaScript Promises, and how do they facilitate asynchronous programming? Explain the 'this' keyword in JavaScript. How does its value change in different contexts? What are some of the new features introduced in ES6 (ECMAScript 2015) and later versions that you find most useful? How do you optimize the performance of a JavaScript application? Describe how you would handle error detection and debugging in a large-scale JavaScript codebase.