// This example is from the book JavaScript: The Definitive Guide.    
// Written by Dog.
// This example is provided WITHOUT WARRANTY either expressed or implied.
// You may study, use, modify, and distribute it for any purpose.        

function f(x, y, z)
{
    // first, check that the right # of arguments were passed.
    if (f.arguments.length != 3) {
        alert("function f called with " + f.arguments.length +
              "arguments, but it expects 3 arguments.");
        return null;
    }

    // now do the actual function...
}