I give you an example how loops are working. Also do a search on the net. Read on what loops are doing. How for-loops are constructed.
What a string is, what an array is and what mathematical operators are and how they work.
Example:
An array is a structure that can store elements. It can be defined enclosing elements in square brackets separated by commas.
Here we have an array of three elements, three individual strings "A", "B" and "C":
var a =
[
"A",
"B",
"C"
];
If you want to alert every element of the array you could do it by using the index of the element in that array:
var a = ["A","B","C"];
var firstElement = a[0];
alert(firstElement);
var secondElement = a[1];
alert(secondElement);
var thirdElement = a[2];
alert(thirdElement);
Counting begins with number 0 in JavaScript.
Note, that an array has a length property.
Now imagine an array of more elements than three. Or a collection of pages of your document.
To make that easier we can do a loop through all the elements using e.g. a for-loop.
We use the value of a.length that is 3 with this example to delimit the number of iterations the loop is doing.
Or all index numbers of the positions of all pages in an InDesign document stored in an array:
var a = app.activeDocument.pages.everyItem().documentOffset;
var allIndexNumbers = a.length;
Back to our little example:
We start with 0, we stop if n < a.length which is 3 is not true anymore, we do baby steps and iterate every integer number from 0 on.
Then we stop. 2 < 3, that's true, but the next step, 3 < 3 is false. And 3 is the length of the array.
var a = ["A","B","C"];
for(var n = 0; n < a.length; n = n+1)
{
alert(a);
};
Just fire up the ESTK (ExtendScript Toolkit app) that is installed with every install of InDesign.
To work with the following code you need not to connect the ESTK with InDesign.
Just watch what the JavaScript Console will show when running the code.
To output something to the console we need method $.writeln() . That's more convenient that memorizing alerts.
Do we need an array we could loop through to get output?
No. We just need numbers for the start, the stop condition and the iteration steps:
// Example 1:
for(var n=0;n<13;n=n+1)
{
// Just show the numbers the loop is doing in the Console:
$.writeln(n);
};
// Needed to prevent any output to the Console at the end of a script that returns something
exit();
Output can be expected as:
0
1
2
…
12
Now we are doing some changes.
1. We introduce a counter.
2. We make more clear what the step mechanism does in a for-loop.
For that we declare one variable each and work with the values of that variables.
// Example 2:
// Assign the value 2 to a variable named steps:
var steps = 2;
// Assign the value 1 to a variable named counter:
var counter = 1;
// Here I substituded the last number in the third part
// of the control structure of the loop with the variable:
for(var n=0; n<13; n=n+steps )
{
//Output will be the word "loop: " plus the value of counter:
$.writeln("loop:"+counter);
//Just write the value of n to the console:
$.writeln(n);
//Build a sum with value n and number 1 and write that to the console:
$.writeln(n+1);
//Build a sum with value of n and the value of steps and write that to the console:
$.writeln(n+steps);
// Changing the counter for every loop that ran.
// Count it up by 1:
counter = counter+1;
};
// Needed to prevent any output to the Console
exit();
Just test if you do changes to the initial value of variable steps. Use 3 as value. Use 4 as value.
Substitute the stop condition, that 13, with the number of pages in your document:
var doc = app.activeDocument;
var numOfPages = doc.pages.length;
Note:
You can concatenate things with the + operator. But you also can build a sum with the same + operator.
Concatenating numbers to get a string:
Adding two items to an empty string will result in a string. Item one is a number, item 2 is a number.
""+1+2 => "12"
Building a sum first and then do a string of it.
JavaScript will first do the mathematical operation and then conactenates the number to the empty string if the operation is enclosed in round brackets:
""+(1+2) => "3"
$.writeln( something );
is a method to write strings to the JavaScript Console of the ESTK.
But beware, that $.writeln() is clever.
It will take everything that is defined and writes a string of it to the console.
Example:
$.writeln(app.activeDocument);
will return "[object Document]"
$.writeln(1+1);
will return "2". It will do the mathematical operation first and then writes a string to the console.
Hope, that helps you getting started.
Regards,
Uwe
PS: If that all is too much work for you changing your script that is working with 2 pages of each export to a script that is working with 4 pages of each export you could always hire a script writer with experience InDesign scripting.
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