InDesign Script error 21

[Serenity McLean]

I had this working the other day before upgrading my version of InDesign. Now it doesnt work. Not sure if that's related. This little script throws a script error 21 on the line:

myParas[i].parentTextFrames[0].parentPage.appliedMaster = myDocument.masterSpreads.item("MC-Chapter");

I have double checked the correct spelling MC-Chapter. Any thoughts?

var myDocument = app.activeDocument;
var myParas = myDocument.stories.everyItem().paragraphs.everyItem().getElements();
var myPage = myDocument.pages;

for (i=0; i<myParas.length; i++)
{
    if(myParas[i].appliedParagraphStyle.name == "Chapter Title" || myParas[i].appliedParagraphStyle.name == "Chapter Number")
    {
    myParas[i].parentTextFrames[0].parentPage.appliedMaster = myDocument.masterSpreads.item("MC-Chapter");
    }
}
alert("Done");

[brian_p_dts]

Not sure what error 22 is, but if a text frame is on the pasteboard, you will get an error because that frame has a null parentPage.

[Manan Joshi]

If the suggestion from @brian_p_dts does not work for you then share the document and we shall be able to resolve the problem or let you know the reasons of the problem.

-Manan

[Serenity McLean]

I've attached the file

[Eugene Tyson]

Not sure if this works for you - but I have terrible trouble making scripts (I'm not that good) but I've started adding alerts to see where I go wrong
It might throw up where the issue is occurring. 

var myDocument = app.activeDocument;
var myParas = myDocument.stories.everyItem().paragraphs.everyItem().getElements();
var myPage = myDocument.pages;

for (var i = 0; i < myParas.length; i++) {
    try {
        var para = myParas[i];
        if (para.appliedParagraphStyle.name == "Chapter Title" || para.appliedParagraphStyle.name == "Chapter Number") {
            // Check if parentTextFrames and parentPage exist
            if (para.parentTextFrames.length > 0) {
                var parentPage = para.parentTextFrames[0].parentPage;
                // Check if parentPage is a valid page
                if (parentPage && parentPage.constructor.name === "Page") {
                    var masterSpread = myDocument.masterSpreads.item("MC-Chapter");
                    // Check if masterSpread is valid
                    if (masterSpread.isValid) {
                        parentPage.appliedMaster = masterSpread;
                    } else {
                        throw new Error("Master Spread 'MC-Chapter' is not valid.");
                    }
                } else {
                    throw new Error("Parent Page is not valid.");
                }
            } else {
                throw new Error("Paragraph is not within a text frame.");
            }
        }
    } catch (e) {
        alert("Error processing paragraph " + (i + 1) + ": " + e.message);
    }
}
alert("Done");

I 

[Serenity McLean · Accepted solution]

Thanks everyone! I resolved my issues with a different appraoch to the problem and have working code now that will apply odd and even masters to the document starting at a user defined page. For anyone looking to do the same, here's what works for me.

//applies left and right masters

var document = app.documents[0];
var masterSpreads = document.masterSpreads;
var pages = document.pages;
var master1Name = "MR-Right";
var master2Name = "ML-Left";

x = prompt ('What is the starting page of range?', '')
x = x-2

//applies to all right pages
for (var n = x; n < pages.length; n++) {
if (n % 2 === 0) {
pages[n].appliedMaster = masterSpreads.itemByName(master1Name);
}
};

x = x+1
//applies to all left pages
for (var n = x; n < pages.length; n++) {
if (n % 2 != 0) {
pages[n].appliedMaster = masterSpreads.itemByName(master2Name)
}
};

alert("Done");

[brian_p_dts]

Just as an FYI, page has a .side property that returns an enum of a few different page positions including recto and verso

[Serenity McLean]

Oh that would be great Brian, That would simplify things! what is the format of that?

[rob day]

Hi @Serenity McLean , In case @brian_p_dts doesn’t reply right away here’s the page API:

https://www.indesignjs.de/extendscriptAPI/indesign-latest/#Page.html

so:

var pgs = document.pages.everyItem().getElements();

for (var i = 0; i < pgs.length; i++){
    $.writeln(pgs[i].side)
    //returns RIGHT_HAND or LEFT_HAND for a facing page doc
};   

[Anantha Prabu G]

I have checked the above code. It's working fine. Could you please tell me which InDesign version you are using?

Indesign 2021
16.3.2

[Serenity McLean]

InDesign 2023

18.5.2

I upgraded from 2021, 16.4.3