Simple beginner script problem

Question

I'm reading Scripting InDesign CS3/4 with Javascript from O'Reilly and this simple example doesn't seem to work. Can someone please see what's up?
Another useful application of split () and join () is processing paragraphs in a text frame. To see how this works, create a new InDesign document; draw a text frame big enough to hold about half a dozen names; and type a list of half a dozen names, one a line. Select the text frame or place the cursor somewhere in the list. The following script sorts the list alphabetically:
// check that a story is selected
if (app.selection[0].parentStory.constructor.name!="Story")
exit ( );
// create an array of paragraphs by splitting the story on hard returns
myArray = app.selection[0].parentStory.contents.split ("\r");
// sort the array
myArray.sort ( );
// join the array as one string separated by hard returns
myString = myArray.join ("\r");
// replace the contents of the selected story with myString
app.selection[0].parentStory.contents = myString;

Answer 1

It highlights
if (app.selection[0].parentStory.constructor.name!="Story")
and says undefined is not an object
Edit: solution, I had to choose Adobe InDesign CS5 from the ESTK menu instead of ESTK CS5