A function is said to be recursive if it calls itself from within its own code block. Although recursion can be a powerful tool, caution must be exercised with its use. Like a loop, a recursive function must always move to satisfy an ending condition. Finally, recursive function calls require great amounts of system resources and memory, so should be used sparingly.

I/O functions

The JavaScript language includes several methods to facilitate program I/O:

• The write() method writes HTML text to the current document
• The writeln() method is similar to the write() method, except that it adds a carriage return to the end of the string
• The alert() method displays a dialog box containing the string argument to the method, and an OK button.
• The confirm() method is similar to the alert() method, except that it also includes a cancel button.
• The prompt() method accepts two arguments - the string to display, and the default text - and includes a text box for user input.

Top-down approach to programming

Solving complex problems can be facilitated by using the top-down method of preparation. The first step is to write the objective on a piece of paper. The next step is to break the task down into two or more component tasks. Each task should be further simplified until it cannot be broken down any further. Finally, each individual task should be implemented in code and then rigorously tested. Finally, the complex problem can be solved by piecing together the individual pieces.