The push() method in JavaScript can be used to add new elements to the end of an array. This method modifies the original array and is commonly used when you want to add elements to the end of an array, expanding its length. For example, myArray.push('newElement') would add 'newElement' to the end of myArray.

In a switch statement, you can use strings, numbers, and symbols as values for case comparisons. These values are compared strictly, meaning both value and type must match for the associated code block to execute.

To select all input elements within a specific form, you should use the querySelectorAll('form input') method. This allows you to target input elements that are descendants of a specific form element. The other options are incorrect because they either select all input elements on the page or attempt to select a form element by ID or tag name, which doesn't filter the input elements within it.

Closures in JavaScript facilitate patterns like the Singleton Pattern, Module Pattern, and Observer Pattern. These patterns use closures to encapsulate data and create private scopes. However, the Factory Pattern is not primarily facilitated by closures. The Factory Pattern focuses on creating and returning objects or instances, which can be achieved without closures. It relies more on object creation and instantiation rather than scope encapsulation.

When 'this' is used inside a function declaration, it typically refers to the global object (e.g., 'window' in a browser), which can lead to unexpected behavior in some cases. In contrast, 'this' inside a function expression refers to the local context where the function is defined, making it more predictable and controllable.

The traditional "for" loop in JavaScript consists of three main parts separated by semicolons. These parts are: initialization (executed once at the beginning), condition (checked before each iteration), and increment (executed after each iteration). The fourth option is incorrect because a "for" loop in JavaScript does not typically have four main parts.

JavaScript is primarily a web-based language used for front-end development to make web pages interactive. Tasks like Web Animations, Form Validation, and Fetching & Displaying Data are core uses. Data Analysis is typically done using languages like Python.

In JavaScript, you can use the querySelector() method to select an element within a specific parent element. This method allows you to specify a CSS selector that matches the desired element. For example, parentElement.querySelector('.child') will select the first child element with the class 'child' within parentElement.

You might prefer to use a function expression (a regular function) over an arrow function when you need to explicitly bind the this context, especially in cases where you want to define methods inside objects or use constructors. Function expressions allow you to use the this keyword as expected, while arrow functions inherit this from their lexical enclosing context.

The value of rest will be [30, 40, 50]. This code uses destructuring assignment to assign the first two elements to a and b, and the rest of the elements to rest using the rest parameter (...). So, a will be 10, b will be 20, and rest will contain [30, 40, 50].