[JS][CS5] question, and comments

Question

HI All.
I must first start off by recommending anyone seriously wanting to get into Scripting, or (like me) am fairly knowledgable, but needed the resource, to check out "InDesign CS5 Automation Using XML & Javascript" by Grant Gamble. (Amazon, Kindle etc...)
I am sure I am not the only one who has made his way, stumbling and even hacking through code to produce scripts that work well, but not really understanding why certain things were done in a certain way. This books helps a great deal with this, laying a good basis for further development.
Anyway, on to my question. In the afore mentioned book, he talks about making a global variable/object that is used to pass variables into throughout the script ie:
var g = {};
main();
g = null;
function main(){
//code here
//g.win = new Window("dialog",undefined,"New Window");
//etc.....
I can see how this works, with "g" being a master item, but why would this be needed? It seems more confusing to me, but maybe cause I am self taught, and not really been shown the "proper" way to use variables!
Can someone explain the reason behind this for me.
Many Thanks
Roy

Answer 1

Hi, Roy:
   I'm going to try again.
    Don't fool yourself. A difference of opinion doesn't mean both sides are right. It could well mean one side is wrong. (Maybe that's me. Maybe that's Jongware. Let's wait and see what he has to say.)
    In this case...this design pattern is just dumb. Unless there's something you're not showing us, like multiple functions that need to exchange data...in which case there is probably a better way, but it's hard to evaluate.
    The pattern is dumb because it does bad things with no upside. It makes the code harder to read. It adds potential conflicts with other scripts. And it has no benefit.
    I should probably have given you yet another example of something better. The very simple one. It's not as good because it still pollutes the namespace with main, but it's easy to understand and to read:
main();
function main() {
   var g = {};
   g.win = new Window("dialog", undefined, "New Window");
Even ignorance of a fnuction is probably better, since you could wrap it in a function later on (as your program got more complex) and it would all still work. That is:
var g = {};
g.win = new Window("dialog", undefined, "New Window");
But I suspect you're oversimplifying the program, since you told us that the point of this "technique" was to "pass variables into throughout the script."
But your example doesn't demonstrate any "passing." It's not too clear exactly what you mean though.
But here are some examples:
var g = {};
f1();
f2();
function f1() {
  g.able = "baker";
function f2() {
  alert(g.able);
There we have some data moving from f1() to f2(). But it's still poor. You should write it like this:
main();
function f1() {  return "baker";
function f2(s) {
  alert(s);
function main() {
  var tmp;
  tmp = f1();
  f2(tmp);
But if for some reason it was really complicated and you needed to have f1() and f2() messing around directly with the data, then you could have a variable that was scoped to both of them:
function main() {
  var shared;
  function f1() {
    shared = "baker";
  function f2() {
    alert(shared);
  f1();
  f2();
main();
But still you would never set a variable to null when you were done. The language has much better features than that! Use them!
When the enclosing function exits, there's never any fear of anything else gaining access to the variable. No need to set its value, because nothing can access it! Cross the final } and you're set. Awesome!
Obviously you put yourself at a level greater than someone needing
this book, but I know my short comings, and can see HUGE value in a book
detailing why certain practices are carried out
Respectfully, this is not a reasonable answer.
There are a lot of books out there. That you have found one that is better than forum posts does not mean it is a good idea to recommend it, especially when it seems to have problems. If you've read through several books and found this one to be better than the others, then that might be a good basis to recommend it. Or if you have searched high and low for books and failed to find any. Or if you were comparing it to Adobe's documentation on scripting. But by all means, do tell us the standard of comparison you're using...
But it doesn't sound like you're doing that. It sounds like you're in one breath praising a book, without comparing it to anything else. And in the next breath, you're asking a question (rightly so!) about what appears to be a bad practice that is advocated by the book.
That just doesn't make much sense.
I hope I'm misinterpretting you.