The global forEach function allows us to enumerate any object according to it’s type. If the object is array-like (has a length property) then we enumerate it like an array. All other objects are enumerated using the standard for var x in y mechanism.
Higher Order Programming is the ability to use functions as values. So you can pass functions as arguments to other functions and functions can be the return value of other functions. This style of programming is mostly used in functional programming, but it can also be very useful in 'regular' object oriented programming.
An example of looping through all the form fields could be checking and unchecking all the check boxes present on a page (checking all the records to delete, or adding all the items to a shopping cart, for instance).
The primary function of a textarea field is to accept input from a form user for the form processing script to do stuff with. You see their use in feedback forms, for example.