These are examples from the book JavaScript: Making Isometric Social Real-Time Games with HTML5, CSS3 and Javascript See the "O'Reilly Policy on Re-Use of Code Examples from Books" (http://www.oreilly.com/pub/a/oreilly/ask_tim/2001/codepolicy.html) for details on how you may and may not use these examples. In most cases, it suffices to simply provide suitable attribution, in the source code and documentation of your program, with a comment like the following: // This code is from the book JavaScript: Making Isometric Social Real-Time Games with HTML5, CSS3 and Javascript // (ISBN #978-1-4493-0475-1). Copyright ??? by Mario Andres Pagella. Please note that the examples are not production code and have not been carefully tested. They are provided "as-is" and come with no warranty whatsoever.