The else if statement is used to specify a new condition to test if the first condition in an if statement is false. It allows for branching in code execution based on multiple conditions. It's a fundamental control structure in JavaScript.

JavaScript's sort() method by default converts elements to strings and then compares their UTF-16 code units. This means that if the array contains mixed data types, the sorting order might be unexpected. For proper sorting, you should provide a compare function as an argument to sort().

When a piece of code returns -Infinity, it is usually due to a division operation where you are dividing a finite number by zero. In JavaScript, dividing any finite number by zero results in -Infinity. Make sure to handle cases where division by zero can occur to prevent unexpected -Infinity values in your code.

In JavaScript, the typeof operator is used to determine the data type of a variable. When var x = "5"; is encountered, the value of x is a string because it is enclosed in double quotes. Therefore, typeof x will return "string". It's important to note that JavaScript is dynamically typed, meaning the type of a variable can change during runtime.

You can add a method to an object in JavaScript by defining a function and assigning it as a property of the object. For example, myObject.myMethod = function() { /* method code */ };. While you can use various patterns and techniques for method definition, there's no standard Object.addMethod() or Object.method() function.

In JavaScript, hoisting is the mechanism by which variable and function declarations are moved to the top of their containing scope during compilation. This means that you can call a function declared with function before it appears in your code, and it will still work. However, it's important to note that only the declarations are hoisted, not the initializations. Understanding hoisting is crucial for writing clean and maintainable JavaScript code.

In AJAX (Asynchronous JavaScript and XML), the XMLHttpRequest object is used to perform HTTP requests asynchronously. It allows you to send and receive data from a server without refreshing the entire web page.

Block scope in JavaScript is introduced using the let keyword, which allows variables to be declared with block-level scope, while const is used to declare constants. The var keyword does not provide block scope and was used in older versions of JavaScript.

Using setInterval with an event-driven approach is a suitable choice for continuously checking and processing incoming messages. This approach allows you to define a specific interval for checking messages, balancing performance and user experience. Options like for...of with asynchronous functions might not provide consistent timing, and do-while with synchronous functions could lead to performance issues. setTimeout with callbacks is more suitable for one-time delays.

In JavaScript, when a function is defined inside another function, the inner function has access to the variables of the outer function due to lexical scoping. Lexical scoping means that the inner function "remembers" the scope in which it was created, allowing it to access and manipulate variables defined in the outer function. This behavior is one of the fundamental aspects of closures in JavaScript.