Array Methods: map, filter, reduce

The `map`, `filter`, and `reduce` methods are the holy trinity of functional programming with arrays in JavaScript. They allow you to process arrays in a declarative style, which is often more readable and less error-prone than using traditional `for` loops. The `map` method transforms an array. It iterates over each element of an array, applies a callback function to that element, and returns a *new* array containing the results of the callback function for each element. The original array is left unchanged, and the new array will always have the same length as the original. The `filter` method creates a new array containing only the elements from the original array that pass a certain test. You provide a callback function that returns `true` or `false`. For each element, if the callback returns `true`, the element is included in the new array; otherwise, it is excluded. The `reduce` method is the most versatile. It executes a 'reducer' function on each element of the array, resulting in a single output value. The reducer function takes an 'accumulator' and the current value as arguments. The accumulator's value is the returned value from the previous iteration. `reduce` can be used to perform a wide variety of tasks, from summing all the values in an array to grouping objects based on a property.